Chin J Plant Ecol-Forthcoming Articles

Effects of different disturbances on plant growth and content of medicinal ingredients of rhizomatous clonal plant Glycyrrhiza uralensis in a natural population

Xuehua YE 薛建国 Xiu-Fang Xie Zhen-Ying HUANG — 2020-09-03 00:00:00.0

Aims Long-term enclosure and grazing prohibition protects Glycyrrhiza uralensis natural population from external disturbances, such as excessive excavation or overgrazing, but it does not the rapid recovery of the damaged G. uralensis natural population. Appropriate external disturbance is always beneficial to plant growth and reproduction, especially for clonal plants such as G. uralensis due to plant clonality. But the roles and mechanisms of disturbance and plant clonality in the recovery of the damaged G. uralensis natural population are still not clear. Methods A natural population of G. uralensis was chosen in the present research, and a field experiment with both clipping (simulated grazing disturbance) and ramet digging out (simulated human excavation disturbance) treatments was conducted to test the effects of different disturbances on plant growth and the content of medicinal ingredients of G. uralensis in the natural population. Important findings The results showed that moderate disturbances, including clipping and ramet digging out treatments, had no significant effects on the ramet density, height and shoot biomass of single ramet of G. uralensis in the natural population, suggesting the same compensation growth in G. uralensis; while G. uralensis showed different responses to severe disturbances, depending on the disturbance type. Significantly lower ramet density, height and shoot biomass of single ramet were observed in G. uralensis under severe clipping treatment, indicating undercompensated growth; while significantly higher ramet height, shoot biomass of single ramet and also total shoot biomass of plant population under severe digging out treatment suggested super-compensatory growth in G. uralensis. Plant clonality, including clonal integration, clonal storage and selective placement of ramets, played important roles in the response of G. uralensis to external disturbance. The content of liquritin and glycyrrhizic acid in taproot of G. uralensis was improved to some extent by external disturbance, thus improving medicinal materials quality.

Response of nutrient characteristics of Achnatherum splendens leaves to different levels of nitrogen and phosphorus addition

Jun-Jun LI Meng-Ru LI Xing-E QI Li-Long WANG — 2020-09-03 00:00:00.0

Aims The nutrient characteristics of nitrogen (N) and phosphorus (P) in plant leaves are affected by the available N, P contents and the N:P in soil, however, little is known about the effects of changes in N, P contents and N:P in soil on N, P nutrient stoichiometry in leaves and nutrient resorption efficiency. Methods In this study, pot experiments were conducted to explore the response of the stoichiometric and nutrient resorption characteristics of Achnatherum splendens leaves to three levels of nutrient addition (low, 1.5 g N?m-2?a-1; moderate, 4.5 g N?m-2?a-1 and high, 13.5g N?m-2?a-1) and N:P (5, 15, 25). Important findings The results showed that increased level of nutrient addition significantly increased the P contents in green leaves and N, P contents in senescent leaves, but significantly deceased the N resorption efficiency (NRE) and P nutrient resorption efficiency (PRE). The increased soil N:P significantly decreased the P contents in senescent leaves and NRE, but increased N:P in green and senescent leaves and PRE. At the same nutrient addition level, soil N:P significantly and positively correlated with PRE, but showed no significant correlation with NRE. At the same level of N:P, the level of nutrition addition was negatively correlated with NRE, but exhibited no significant correlation with PRE. The change of plant demand for N and P caused by changing environment can be indicated effectively by plant leaf NRE:PRE, and the characteristics of nutrient stoichiometry and resorption of A. splendens leaves are affected together by nutrient addition levels and N:P in soil.

Basic characteristics of Stipa sareptana var. krylovii communities in China

lu shuaizhi Xian-Guo QIAO Li-Qing ZHAO WANG Zi GAO Chen-Guang wang jing Ke GUO — 2020-09-03 00:00:00.0

Stipa sareptana var. krylovii Formation is one of the typical steppes endemic to Central Asia. Because the distribution of its eastern border is adjacent to the meadow steppes on the Hulunbeir Plateau, western border extends to the desert steppes on the Ulanqabu Plateau and Tianshan Mountains, southern border lies among the warm temperate steppes on the Loess Plateau, and it also spreads into the alpine steppes on the eastern margin of the Qinghai-Xizang Plateau, S. sareptana var. krylovii Formation has the widest ecological adaptability. In this study, we described and analyzed the eco-geographical distribution, community characteristics and vegetation classification of S. sareptana var. krylovii Formation based on data from 117 surveyed plots. The results showed that there are 336 seed plants belonging to 36 families and 131 genera. The families with more than 15 species are Gramineae, Compositae, Leguminosae, Rosaceae, Chenopodiaceae and Liliaceae. 91.67% of the species are rare species in this Formation with occurrence frequency smaller than 20%. Besides S. sareptana var. krylovii, the most common species are Cleistogenes squarrosa, Heteropappus altaicus, Agropyron cristatum, Koeleria cristata, Potentilla bifurca, Salsola collina, Allium tenuissimum and Leymus chinensis. In addition, Hemicryptophyte is the most common life form, covering 66.37% of the species, xerophytes is the most common ecological type of water, accounted for 66.37% of all species, and east Palearctic was the major floristic geographical element, containing 33.33% of all species. Based on China Vegetation Classification System, S. sareptana var. krylovii Formation could be classified into 6 association groups, 45 associations.

Impacts of global changes on food web structure

Qing-Qing WANG Yan GAO — 2020-09-03 00:00:00.0

The food web sustains its structure mainly by bottom-up and top-down controls, which are based on the interactions between species at different trophic levels. However, global changes can alter interspecific relationships and threaten the maintenance of biodiversity, but it is still unclear how global change alters the structure of the food webs. In recent years, based on numerous studies on food webs composed of multi-trophic levels at large spatiotemporal scales, researchers have found that global changes alter food web structure mainly through three mechanisms: phenological mismatching, loss of key species and biological invasion. Here we focused on these three mechanisms and reviewed how these mechanisms change food web structure change, with further discussion on the driving factors in ecology and evolution. All these three mechanisms can alter the interspecific interactions, resulting in distortion of the regulation of food webs. The major difference among these three mechanisms is how interspecific interactions are changed. Phenological mismatching occurs due to the asynchronous responses in the phenology of different species to global changes, while the loss of key species can change or even entirely destroys some critical feeding/predation relationships, and invasive species often simplify the food web structure by causing strong interspecific competition to exclude species at the same trophic level. Finally, we addressed that the changes in food web structure depends on the adaptation of species to the ongoing global changes and provided some insights into future researches. As the impacts of global changes are increasingly aggravating, it is necessary to further study the mechanisms how global changes influence food web structure, to reinforce the extant theoretical basis for improvements in the strategies of biodiversity conservation and ecological restoration.

Plant size, branch age and environment factor co-drive variations of branch traits of Pinus koraiensis

Qinghan Yu Guang-Ze JIN Zhi-Li LIU — 2020-09-03 00:00:00.0

Aims Variations of many branch traits are affected by plant size, branch age and environment factor, but the importance of these factors to intraspecies variations of branch traits has rarely been evaluated simultaneously. Methods In this study, we took Pinus koraiensis as the research object, to explore the effects of plant size (DBH or tree height), branch age and environmental factors (light intensity, soil nutrient content and water availability) on branch traits, by measuring morphological traits, chemical traits and anatomical traits in different branch ages of 69 individuals with DBH in the range of 0.3-100 cm. Important findings Our results showed that: (1) DBH and tree height had different effects on branch traits: wood density (WD), the xylem area-to-total cross-sectional area ratio (RXA), the phloem area-to-total cross-sectional area ratio (RPHA) and the pith area-to-total cross-sectional area ratio (RPA) were more sensitive to DBH, while the total resin canal area-to-total cross-sectional area ratio (RRC) and wood nitrogen content (WN) were more affected by the tree height; (2) branch age was the most important factor in driving intra-species variations of branch traits of Pinus koraiensis, followed by plant size, while the impact of environment factors was minimal; (3) WD and RPHA were significantly positively correlated with DBH, while RPA were significantly negatively correlated with DBH; and RRC and WN were significantly positively correlated with tree height. Except for WN, the relationships between branch traits and branch age were significant, and as tree growth, the rate of RRC decreasing with branch age was enhanced, but the rate of RPA decreasing with branch age was weaken. The results of our study are helpful to understand the influencing factors of intraspecies variation of branch traits at the local scale and the adaptation mechanism of branches to cope with environmental changes.

Characteristics of soil carbon and nitrogen contents and enzyme activities in sub-alpine secondary forests with different successional stages in Western Sichuan, China

2020-09-03 00:00:00.0

Aims Regenerating sub-alpine forests have an capacity to capture carbon and nitrogen. Our objectives were to quantify variations of soil organic carbon and nitrogen and enzyme activities following natural secondary forest of different successional stages, and to better understand the underline mechanism of secondary forest regulating soil carbon and nitrogen cycling in sub-alpine forest zone. Methods We used the space-for-time substitution method by selecting four sub-alpine secondary forests, composed of 60 (60-NSF), 70 (70-NSF)and 80-years (80-NSF) natural secondary forests at different successional stages with natural regeneration on cutting-blanks, and primitive Abies faxoniana forest (CK) in Miyaluo forest of Western Sichuan, China. The soil samples were taken from 0 to 20 cm depths within each of the forests in late July, 2019, and were transferred to the laboratory. Soil organic carbon (SOC), soil total nitrogen (TN), dissolved organic carbon (DOC) and nitrogen (DON), light fraction organic carbon (LFOC) and soil enzyme activity were measured. The activities of 5 soil extracellular enzymes related to soil carbon and nitrogen cycles were determined to explain their relationships with soil physico-chemical properties. Important findings The contents of topsoil SOC, DOC, LFOC decreased with natural succession, whereas TN and DON were all in the order 60-NSF < 80-NSF < 70-NSF, but 80-NSF and 70-NSF exhibited no significant differences. The topsoil organic carbon and nitrogen and their active fractions in natural secondary forests were lower than those in CK, while no significant differences in DOC and DON contents were observed between 80-NSF and CK. The activities of β-4-glucosidase (βG), β-4-N-acetylglucosa -minidase (NAG) and Polyphenol oxidase (PHO) in CK were significantly higher than those of natural secondary forests, whereas Cellulose hydrolysis (CBH) and Phenol oxidase (PEO) had no significant difference between secondary forests and CK. βG and CBH in 60-NSF were significantly lower than those of 70-NSFand 80-NSF, but activities of NAG in 80-NSF were significantly higher than in 60-NSFand 70-NSF. There was no significant difference in the type of forest PEO. Both Pearson correlation analysis and redundancy analysis showed that soil enzyme activities were significantly correlated with TN, LFOC and DOC contents. TN explained 65.4% of the variations in enzyme activity, and implied that change of soil nitrogen content might affect C-related hydrolytic enzyme activity (e.g. βG、CBH and NAG). Meanwhile soil microorganisms prefer to use readily decomposable carbon and nitrogen. Meanwhile soil microorganisms prefer to use readily decomposable carbon and nitrogen. Therefore, activity of some soil enzymes such as βG, CBH and NAG in natural secondary forests by decreasing TN、LFOC and DOC content. Based on the responses of soil enzyme activity, we conclude that the C and N cycling in primitive forest could be more favorable than secondary forest in the early-successional stage (<60 a) for high-altitude sub-alpine forest ecosystems in western Sichuan, China.

The response of soil net N mineralization to different N levels in saline-alkaline grassland of Northern China

Xiaohui XU Diao Huajie Chuyi Tan Jie Hao Yan Shen Kuanhu Dong Chang-Hui Wang — 2020-09-03 00:00:00.0

With the development of modern industry and agriculture and the combustion of fossil fuels, the amount of atmospheric nitrogen (N) deposition is increasing year by year. These active N gradually change the process and function of the terrestrial ecosystem with the dry and wet N deposition into the soil, and at the same time affect the soil N cycle and the productivity of the ecosystem. The grassland ecosystem in the Agro-pastoral Ecotone in northern China is affected by both agriculture and animal husbandry, and the amount of nitrogen deposition is more than that of natural grassland ecosystem. In the Agro-pastoral Ecotone in North China, salinized grassland is widely distributed, and the degree of soil salinization affects the state of soil nutrients. Therefore, for the salinized grassland ecosystem with poor nutrients, how the atmospheric nitrogen deposition affects the process of soil nitrogen cycle has not been solved yet. Methods An experimental platform was set up to simulate N deposition in the saline alkaline grassland ecosystem in Youyu County, Shanxi Province, 8 N addition levels was designed, expressed by 0, 1, 2, 4, 8, 16, 24, 32 g N m-2 yr-1, evenly spraying the same amount of ammonium nitrate (NH4NO3) at the beginning of each month during growth seasons from May to September. From May of 2017, net N mineralization rates was measured once a month by using top - cover PVC cylinders. The sensitivity of net N mineralization rates were calculated at different N levels. The experiment has conducted for three years from 2017 to 2019. Important findings The results showed that: High nitrogen level (N16, N24, N32) significantly increased the soil inorganic nitrogen pool (P < 0.05); (2) soil nitrogen mineralization in salinized grassland ecosystem was also dominated by nitrification. After three years of nitrogen addition, high nitrogen level (N24, N32) significantly promoted the rate of soil net nitrification, and different nitrogen levels responded differently in different months and years; (3) The sensitivity of soil net N mineralization to different N addition showed significant difference across 3 years with different precipitation. Lower N addition improved the sensitivity of soil net N mineralization, while higher N addition reduced the sensitivity of soil net N mineralization;(4) There was a positive correlation between soil net nitrogen mineralization rate and soil temperature, water content, and a negative correlation with soil pH value. The sensitivity of soil nitrogen cycle to N addition is higher in the saline-alkaline grassland of North China.The influence of N deposition on soil N cycle for the model prediction should be considered in the future.

Stoichiometric characteristics of fine root and rhizosphere soil of Broussonetia papyrifera in karst rocky desertification environment, SW China

Jie Yin Yixin BAI — 2020-08-27 00:00:00.0

Aims The objective of this study was to estimate the adaptive strategies of Broussonetia papyrifera to the poor soil nutrients in karst rocky desertification environment of Southwest China, and the response of stoichiometric characteristics of fine roots and rhizosphere soil to the degree of rocky desertification. Methods Ecological stoichiometry was applied to study the contents of C, N, P, K, Ca and Mg and C:N:P ratios of fine roots and rhizosphere soil of Broussonetia papyrifera in Karst rocky desertification environment of Southwest China. Important findings The results showed that except Ca content, the nutrient contents of the fine roots and rhizosphere soil of B. papyrifera in karst rocky desertification environment were all at a low level. N:P ratio in fine roots was 12.59, indicating that the growth of B. papyrifera was limited by N and P. With the increased of the degree of rocky desertification, the contents of C and N as well as C: N ratio and C: P ratio in fine roots decreased first and then increased, while the contents of K and P increased first and then decreased, but the contents of Ca, Mg and N: P ratio did not change significantly. The contents of N, P, K, Ca in rhizosphere soil showed different trends in the different degrees of rocky desertification, while the contents of C, Mg and C:N:P ratios were relatively stable. Additionally, the contents of C, P, Ca, Mg and C:N ratio and C:P ratio in fine roots were positively correlated with that of corresponding elements in rhizosphere soil, while N content in the fine roots was negatively correlated with that N in the rhizosphere soil. Moreover, the K content of fine roots was relatively stable, hardly affected by the nutrients of rhizosphere soil.

History of Swiss-French School of phytosociology and its influences on modern vegetation ecology

Jian Zhang Kun SONG Yong-Chang SONG — 2020-08-27 00:00:00.0

The Swiss-French School of phytosociology, also known as the Braun-Blanquet School, is prevalent in Europe and is one of the most influential schools in vegetation science. Here we gave a short introduction of the history of the Swiss-French School, its fundamental theory and the field practice. The development of the school can be divided into four periods: establishment (1910–1943), development (1945–1980), transition (1980–1990), and integration (1990–). The school gives emphasis on the importance of field practice, species interactions and community dynamics, and the critical role of character species or diagnostic species in vegetation studies. The school also emphasizes that the main attribute of plant community is species composition, and has developed a detailed workflow of field inventory and vegetation classification. Using the association as the basic unit, it builds a rigorous and formal system for vegetation classification. And the school has the strong compatibility in theory and technique. All these advantages are served as the basis of the development of current vegetation ecology. In addition, we identified several improvements needed or challenges of the school, including the definition of character species and association, data integration and transformation, and the linkage with eco- physiognomic vegetation classification. Finally, we gave a short introduction to the history of the Swiss-French School in China, and discussed its potential to elevate the current vegetation research in China.

Relationships?of?flower?longevity?with attractiveness traits and their effects on female fitness of alpine meadow plants on Qinghai-Tibet plateau

Yu-Xian WANG Meng HOU Yan-Yan XIE Zuo-Jun LIU Zhi-Gang ZHAO Ning-Na LU — 2020-08-10 00:00:00.0

Aims Flower longevity, the length of time that flowers remain open and functional, is an important floral trait that influences plant reproductive success. Prolonging floral longevity can provide reproductive assurance under unfavorable pollination environment, but may suffer some fitness costs. The theoretical models of flower longevity have suggested that there is a trade-off of resources allocation between the flower longevity and attractiveness traits. That is to say, flower longevity can adjust according to resource allocation. To understand the potential adaptive significance of flower longevity, it is necessary to disentangle the potential relationships between flower longevity and attractiveness traits (flower size and number) and their effects on female fitness of alpine meadow plants at inter-species level on Qinghai-Tibet plateau. Methods In the alpine meadows of Qinghai-Tibetan Plateau (2,900 m vs. 3,600 m), we assessed how the relationships between floral longevity and flower attractiveness traits of 11 species varied at inter species level under different pollination contexts. And we quantified the relative contribution of flower longevity and flower attractiveness traits to the female fitness of plants at inter- species level at low and high habitats. Important findings The results show that there is a trade-off between flower longevity and flower number in both low and high altitude communities. And we found that both longer flower longevity and larger flower size increases the female fitness of plants in low-altitude community, However, the female fitness of plants is only associated with flower longevity in high-altitude community. Overall, our results suggest that flower longevity is more important for the female fitness in high-altitude plants than low-altitude plants.Methods We assessed how the relationships between floral longevity and flower attractiveness traits of 11 species varied at inter species level under different pollination contexts (2,900 m vs. 3,600 m). And we also assessed the relative contribution of flower longevity and flower attractiveness traits to the female fitness of plants at inter- species level in different pollination environments. Important findings The results show that there was a trade-off between flower longevity and flower number in both low and high altitude environments. And prolonging flower longevity increases the plant's female fitness. While the female fitness of plants is only associated with flower longevity in high-altitude environment, which suggests that flower longevity is more important for the female fitness in high-altitude plants than low-altitude plants.Methods In the alpine meadows of Qinghai-Tibetan Plateau (2,900 m vs. 3,600 m), we assessed how the relationships between floral longevity and flower attractiveness traits of 11 species varied at inter species level under different pollination contexts. We also assessed the relative contribution of flower longevity and flower attractiveness traits to the female fitness of plants at inter species level in different pollination environments. Aims Floral longevity, the length of time that flowers remain open and functional, is one trait known to have important consequences for pollination success. Prolonging floral longevity is a strategy for plants to ensure reproductive success under unfavorable pollination environment, however, it will increase the cost of reproduction. The theoretical models of flower longevity have suggested that there is a trade-off of resources allocation between the flower longevity and attractiveness traits.We aim to test the relationships between flower longevity and attractiveness traits (flower size and number) and their effects on female fitness of alpine meadow plants at inter-species level on Qinghai-Tibet plateau. Methods We assessed how the relationships between floral longevity and flower attractiveness traits of 11 species varied at inter species level under different pollination contexts (2,900 m vs. 3,600 m). Furthermore, we assessed the relative contribution of flower longevity and flower attractiveness traits to the female fitness of plants at inter- species level under different pollination environments. Important findings The results show that there is a trade-off between flower longevity and flower number in both low and high altitude environments. And prolonging flower longevity increases the female fitness of plants. While the female fitness of plants is only associated with flower longevity in high-altitude environment, which suggests that flower longevity is more important for the female fitness in high-altitude plants than low-altitude plants.

Soil enzyme activities and their influencing factors among different alpine grasslands in the Qinghai-Tibet Plateau

Ziwei Wang Songze Wan Hongmao Jiang Yang Hu Shuqin Ma Youchao Chen Xuyang Lu — 2020-08-10 00:00:00.0

Aims As a key factor of nutrient cycling in ecosystem, soil enzyme activity is an important indicator of soil quality and ecosystem function. However, there were few studies on the differences of soil enzyme activities among different alpine grassland ecosystem types. Thus, the aims of this study were to compare the differences of soil enzyme activities among five different alpine grassland types and to reveal their influencing environmental factors in the Qinghai-Xizang Plateau. Methods 21 samples of five alpine grassland types, including alpine meadow (AM), alpine steppe (AS), alpine meadow steppe (AMS), alpine desert steppe (ADS) and alpine desert (AD) in northern Qinghai-Xizang Plateau, were selected for field in-situ investigation and sampling. The activities of 14 enzymes involved in the cycling of carbon (C), nitrogen (N) and phosphorus (P) were determined, and the relationships between enzymatic activities and environmental factors in alpine grassland were established. Important findings The activities of C-acquisition (invertase, cellulase, β-1,4-glucosidse, polyphenol oxidase and peroxidase), P-acquisition (alkaline phosphatase) enzymes and two N-acquisition (arylamidase and nitrite reductase) were significantly different among different alpine grassland types. And the correlations were found among C-acquisition, N-acquisition and P-acquisition enzymes. A significant positive correlation was found between invertase and alkaline phosphatase, between cellulase and N-acetyl-α-D-glucosaminidase. A significant negative correlation was found between polyphenol oxidase and nitrite reductase, N-acetyl-β-D-glucosaminidase. Soil organic matter (SOM) content, gram negative bacteria (G-) content, ratio of nitrogen to phosphorus (N:P), gram positive bacteria (G+) content, bacteria content, actinomycetes content, total nitrogen (TN) content and fungi content were the key factors which influencing soil enzyme activity among the 19 environmental indicators, and SOM content had the greatest impact (explains 11.9%). The results demonstrated that the activities of C-acquisition, P-acquisition and two N-acquisition (arylamidase and nitrite reductase) enzymes were significantly different among different types of alpine grassland. And soil enzyme activities were mainly controlled by SOM content, microbes and N elements in alpine grassland ecosystems. The results of this study will provide a scientific reference for predicting soil enzyme activity in the alpine grassland ecosystem of the Qinghai-Xizang Plateau and its response to global changes, and provide a theoretical basis for maintaining the primary productivity of alpine grassland ecosystem.

Effects of dissolved organic matter from different plant sources on soil enzyme activities in subtropical forests

2020-08-10 00:00:00.0

Aims This study aims to explore the effects of dissolved organic matter (DOM) from different plant sources on subtropical forest soil enzyme activities in order to provide a scientific basis for soil carbon cycling under rainfall leaching conditions in different forest ecosystems of subtropical areas. Methods Three kinds of DOM, extracted from the fresh leaves of Cunninghamia lanceolata, Schima superb, and Phoebe zherman, were added to the soils of ??C. lanceolata plantation. Soil treated with deionized water of the same amount as the DOMs’ served as the control. Soil incubation of treated and control soils was conducted for 25 days in the laboratory. The physical and chemical properties, microbial biomass, and enzyme activities of the soils were determined after incubation. Important findings The results showed that, compared with the control treatment (CT), the soil total organic carbon (SOC), soil total nitrogen (TN) content, and carbon-nitrogen ratio had no significant changes after adding DOM. However, the TN content of the treatment with added DOM from ??C. lanceolata leaf DOM (CL) was significantly lower than those of treatments with added S. superb leaf DOM (SL) and P. zherman leaf DOM (PL), and the carbon-nitrogen ratio in CL was significantly higher than that in SL and PL. The three treatments with added DOM increased soil dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) con-centrations overall. There was no significant change in soil microbial biomass carbon (MBC) concentration after all three DOM inputs, while the microbial biomass nitrogen (MBN) concentration in C. lanceolate leaf DOM input (CL) and S. superba leaf DOM input (SL) treatment was reduced by 50.9% and 51.1%, respec-tively, compared to control treatment (CT). However, MBN concentration in PL treatment was increased by 54.0% than CT. DOM input significantly increased the enzymatic activities of β-glucosidase, cellobiohydrolase, and peroxidase in comparison with CT, but significantly decreased the activity of polyphenol oxidase. In ad-dition, both β-glucosidase and cellobiohydrolase activities showed the following characteristics: CL > SL >PL. The results of a correlation analysis showed that the content of SOC, TN and MBN and the activity of β-glucosidase and cellobiohydrolase of the treatments with DOM were significantly correlated with the DOC content and humification index (HIX) of the added DOM. In addition, the content of soil MBN and polyphenol oxidase activity were positively correlated with the pH value of the added DOM. The results of redundancy analysis (RDA) showed that the key factors causing the change in soil enzyme activities after DOM input were DON and DOC. In general, differences in the properties of DOM obtained from different plant sources affect the activities of soil carbon cycling hydrolase. DOM input increases the availability of soil carbon and nitrogen, and elicits different responses from the four carbon harvesting enzymes. This provides the theoretical basis for exploring the process of carbon cycling in the rain-rich subtropical forest ecosystem.

The effect of soil organic matter chemical compositions on soil protease and urease activity of alpine grassland soils in Northern Tibet, China

Shuqin Ma Ziwei Wang Youchao Chen Xuyang Lu — 2020-08-07 00:00:00.0

Aims Soil enzymes play an important role in the process of soil nutrient transformation. The main purpose of this study is to explore the soil organic matter chemical compositions and its effect on soil protease and urease activity in alpine grasslands in Northern Xizang, China. Methods The pyrolysis Gas Chromatograph/Mass Spectrometer (Py-GC/MS) was used to obtain the chemical compositions of soil organic matter, and to analyze the relationships between soil chemical compositions and soil enzyme activity from five alpine grasslands, including alpine meadow, alpine grassland, alpine meadow grassland, alpine desert grassland and alpine desert in Northern Xizang, China. Important findings The results showed that the enzyme activities among five alpine grassland soils (0-15 cm) were different. The urease activity in the soil of alpine desert steppe was significantly higher than protease, while the difference between the urease and protease activities of other types of alpine grassland did not reach statistical significance. The difference of soil protease activity was significant difference among five alpine grassland types, while the difference of soil urease activity was not significant. The correlation analysis showed that the protease activity was closely related to the relative abundance of alkanes, alkenes and aromatics in soil organic matter and the ratio of furfural to pyrrole. Nevertheless, the correlation relationships between urease activity and soil organic matter chemical compositions were not significant. The results indicated that alpine grassland type and soil organic matter chemistry were the key factors affecting soil protease activity rather than soil urease activity, hence the urease activity of alpine grassland soils and its influencing factors needed further study.

Characteristics of Stipa bungeana Communities in China

Xian-Guo QIAO Ke GUO Li-Qing ZHAO WANG Zi Chang-Cheng LIU — 2020-08-07 00:00:00.0

Stipa bungeana Formation is one of the main steppes in Eurasian. Being endemic to China, it distributes mainly in the Loess Plateau and its surrounding area. The current status of its distribution is noted to have shrunk and highly fragmented due to conversion to cropland or unstable successional stage. In this study, we described and analyzed the eco-geographical distribution, community characteristics and vegetation classification of S. bugneana Formation based on data from 108 plots surveyed during 2013-2019. Our results showed that S. bungeana Formation was mainly distributed in the north of Shaanxi, the south of Ningxia, the east and middle of Gansu, the north of Shanxi, the loess hills in the south of Yinshan Mountains and the Erdos Plateau. This Formation occurred mainly on loess soils or kastanozems, and its distribution elevation ranged from (1) 631 - 3174 (4098) m. 214 plants belonging to 37 families and 109 genera were recorded, with most of them are rare species in the Formation. Hemicryptophytes or perennial forbs have more species than other life forms. Xerophytes, especially meso-xerophytes and typical xerophytes have the highest richness in species than mesophytes. Among the 10 floristic geographical elements, East Asia element, East Palearctic element and middle Asia element were the three major floristic elements. The height, cover, biomass and richness of plots had a rather large range because those values depended highly on the moisture and disturbance intensity of habitat. Based on China Vegetation Classification System, S. bugneana Formation could be classified into 7 association groups, 37 associations.

Effects of gradient warming on biological soil crust-soil system respiration in alpine sandy area

2020-07-31 00:00:00.0

Abstract Aims Biological soil crust is an important type of surface cover in alpine sandy areas. Studying the effect of warming on respiration from biological soil crust-soil system in alpine regions can provide a certain reference for accurately assessing the response and feedback of biological soil crusts to climate change in alpine ecosystems. Methods The moss and algae crusts in the artificial vegetation restoration area were taken as the research object. The passive warming device OTC was used to simulate the gradient warming. The daily and growing season dynamics of respiration rate of two types of biological soil crust-soil system under the condition of experimental warming were observed. The effects of warming on CO2 emission and temperature sensitivity were discussed. Important findings The daily and growing season dynamic characteristics of respiration rate of moss and algae crust-soil system were not changed by warming, which showed a “single-peak” curve. The daily dynamic peaks appeared around 13:00, and the dynamic peaks of growing season appeared around August; The warming changed the daily dynamic peak of respiration rate of biological soil crust-soil system. Under relatively dry years (2017), moderate warming increased the cumulative CO2 emission of two types of biological soil crust-soil system during growing season, while the excessive warming decreased the increase of the two types of biological soil crust-soil system; Under relatively wet years (2018), the greater the warming, the greater the CO2 emission of two types of biological soil crust-soil system increased. The exponential function could better describe the relationship between respiration rate and temperature of two types of biological soil crust-soil system. Under relatively dry years, the higher the increase of temperature, the smaller the temperature sensitivity of moss and algae crust-soil system respiration, the temperature sensitivity varied from 1.47 to 1.61 and 1.60 to 1.95 respectively; Under relatively wet years, the higher the increase of temperature, the larger the temperature sensitivity, the temperature sensitivity varied from 1.44 to 1.68 and 1.44 to 1.76 respectively. This study shows that global warming has greatly increased the respiration of biological soil crust-soil system in alpine ecosystem, Therefore, when accurately evaluating the carbon cycle process of alpine ecosystem, we should fully consider the impact of climate warming on the wide spread biological soil crusts in this area.

The key characteristics for facilitating Leucaena leucocephala to successfully invade pioneer community of tropical monsoon forest

Jinhuan LUO Zhaoyuan Tan Bin CHEN Guangwu CHEN Kai JIANG Fang QiHe Hui Zhang — 2020-08-20 00:00:00.0

Aims Due to fast-growing and high drought stress tolerance, Leucaena leucocephala has been widely used for afforestation in degraded tropical forests worldwide, but it is also a global invasive exotic species. Studies have shown that fast-growing can help Leucaena leucocephala successfully invade subtropical forest. In this study, we aimed to investigate whether fast-growing and high drought stress tolerance can help Leucaena leucocephala invade tropical monsoon forest. Methods The pioneer community of tropical monsoon forest which had been invaded by Leucaena leucocephala in Baopoling Mountain, Sanya, China was the research object. Through the t-test to compare the differences in key functional traits that were related to growth rate (photosynthesis rate, stomatal conductance and transpiration rate) and drought stress tolerance (leaf turgor loss point) in both wet and dry season between Leucaena leucocephala and eight dominant native species of pioneer community of tropical monsoon forest. And principal component analysis (PCA) was used to investigate whether these functional traits can best discriminate between Leucaena leucocephala and the eight dominant native species. Important findings Leucaena leucocephala could invariably fast-growing (photosynthesis rate, stomatal conductance and transpiration rate much higher than native species) from wet to dry season and had higher drought stress tolerance (leaf turgor loss point much lower than native species) in the dry season. The results of PCA showed that these functional traits could significantly discriminate between Leucaena leucocephala and the eight dominant native species. Therefore, invariably fast-growing from wet to dry season and high drought stress tolerance in the dry season make Leucaena leucocephala successfully invade pioneer community of tropical monsoon forest. In the future, these functional traits can be used to select many native species to perform biological control of Leucaena leucocephala in other tropical forests.

Dynamic characteristics of metal element content and return of Casuarina equisetifolia litter at different distances to the coastline

Feng YUAN Mao-jin LI Chuan-yang Jiang Na HeLIU Kunlin Li Tao Hong — 2020-07-28 00:00:00.0

Aims Accurate estimation of the variation of nutrient cycling along environmental gradients within an ecosystem is important for assessing their ecological functions. The aim of this study is to explore the effects of different habitats on the metal element content and nutrient return dynamics of Casuarina equisetifolia. Methods Taking the litter of C. equisetifolia in Chihu State-owned Protective Forest Farm of Huian, Fujian Province as the research object, five distances named T1, T2, T3,T4 and T5 respectively were selected in order of near to far from the coastline, and the litter was collected to determine the metal element content. Important findings. We found that: 1) Different coastal distances had significant effects on the content and return of each element of C. equisetifolia litter. The element content and return from the forest edge zone to interior forest were linear. Fe, Cu, Zn and Mn increased since T4, and their changing trend and amount of the return and content along the gradient were similar. 2) There were significant differences on the content of litter elements among different months. Litter Na, Fe, Cu, and Zn had similarities, and had lowest value in June and November. Litter Mn fluctuated after falling from February to April. The return amount was generally similar between litter Na and Cu, with peaks in May, August, and January; Litter Mn, Fe, and Zn showed similar return amount, with peaks in May, August, and January. 3) Na in soils at different distances from the coastline decreased gradually, while other elements fluctuated and did not show significant difference along the gradient. 4) Litter Na and Fe were significantly positively correlated, and litter Na and Zn, Fe and Cu, and Fe and Zn were extremely significantly positively correlated, respectively. There was a positive correlation for the same element between soil and litter and the correlation was significant for Na and Cu. The difference in litter element was greatly affected by the difference in resorption rate during litter falling at different timing along the distance gradient. The temporal difference among different months was due to the requirements from plant life activity. The difference in the return of the element was related to the amount of litterfall and the content of elements in the litter.

Effects of mating distance and number of pollen donor on sexual reproduction of Sagittaria trifolia

Pan-Pan ZHOU Quan CHEN Yu-Jie ZHANG — 2020-07-27 00:00:00.0

Aims Sexual reproduction is the core of plant life history and evolution. Besides the influence of maternal genotype and environment, the contribution of paternal parts on reproduction should not be ignored. In particular, the distance and diversity of pollen donor have significant impacts on fruit setting and offspring quality, which often show distinctive patterns due to specific reproductive characteristics and evolutionary processes of different species or populations. Our objective was to study the effects of mating distance and number of pollen donors on reproductive performance of Sagittaria trifolia. Methods Three mating distances including selfing, outcrossing of short distance (<50 km), and outcrossing of long distance (>200 km) and two types of pollen donors (single and double donor) were investigated in S. trifolia using hand-pollination. Besides selfing, the remaining factors formed a factorial design, resulting in a total of five pollination treatments. We analyzed the differences in fruiting probability, seed number per fruit, seed size, germination rate of F1 seed (year 2018 and 2019) and their seedling length (year 2018 and 2019) . Important findings Different mating distances had no significant effects on fruiting probability, seed number per fruit, seed size, germination rate or seedling length of S. trifolia, implying that there was no inbreeding or outbreeding depression in this species. The increase from single to double pollen donors had no effect on seed production of S. trifolia, but seed germination rate in double-donor treatment was slightly higher than that of single-donor. All together, mating distance and number of donors had little influence on reproductive performance of S. trifolia, which might be related to frequent selfing history, long-distance gene dispersal and high similarity in aquatic habitats in this species. Meanwhile, this study was based on mutual mating designs between genotypes from over 20 natural populations. Such results also imply high and stable reproductive output of S. trifolia at species level.

Effects of atmospheric compound pollution on photosynthesis of poplar leaves

Jing Li Xin WANG Zhenhua Wang Bin Wang Chengzhang Wang Meifeng Deng Ling-Li LIU — 2020-07-10 00:00:00.0

Aims Rapid economic growth resulted in serious atmospheric compound pollution in China. Ozone and aerosol are the two major pollutants which could greatly alter plant photosynthesis, with excessive ozone inhibiting leaf photosynthesis via phototoxic effect and aerosol tending to increase it by diffuse radiation fertilization effect. This paper aims to investigate the relative impact of ozone and aerosol on leaf photosynthesis under atmospheric compound pollution. Methods We planted Populus × canadensis at three sites along the air pollution gradient around Beijing. During the growing season of 2012-2013, ozone concentration (AOT40), aerosol optical depth (AOD), air temperature, photosynthetically active radiation (PAR) and photosynthetic rates of leaves were measured at these sites. Important findings The results show that: (1) Pollutant loadings were closely related to meteorological factors. AOT40 increased with increasing air temperature and AOD. Aerosol loadings reduced the external canopy PAR but increased internal canopy PAR. (2) Compared to the negative effects of AOT40, AOD and air temperature had significantly positive effects on photosynthesis of sun leaves. Photosynthetic rates of shade leaves was positively correlated with AOD. (3) For sun leaves, ozone was the most important factor affecting their photosynthetic rates. Aerosol's positive effect on photosynthesis of sun leaves was compensated by the negative effect of ozone to a certain extent. Meanwhile, by scattering solar radiation, aerosol contributed the most to the increased photosynthesis of shade leaves. Our study partitioned the effects of ozone and aerosol on leaf photosynthesis. We found that atmospheric compound pollution induced different impacts on the photosynthesis of sun and shade leaves, suggesting that plants with different canopy structures may respond differently to compound pollution. Our results also indicate that aerosol and ozone pollution need to be controlled simultaneously to protect the productivity and function of ecosystem.

The effects of altered litter input and nitrogen addition on ecosystem aboveground primary productivity and plant functional group composition in a semiarid grassland

2020-07-09 00:00:00.0

Aims Litter is the major input source of soil organic carbon and nutrients in natural ecosystems and considered as a key link between above- and below-ground carbon cycles. Changes of litter input amount have been proven to exert significant impacts on plant productivity, community structure, and therefore ecosystem function. In Inner Mongolia semiarid grasslands, different grassland management practices such as grazing, clipping, and fencing have caused dramatic changes in litter production and input. In addition, as a nitrogen-limited ecosystem, Inner Mongolia semiarid grasslands also experienced increasing nitrogen deposition. However, how do changes in litter input and nitrogen addition impact the community productivity and composition of plant functional groups are still unclear in the semiarid grasslands. In this study, our objectives are: 1) Investigate the effects of altered litter input and nitrogen addition on community productivity; 2) study the changes in aboveground biomass of different plant functional groups and their contribution to community productivity under different litter input and N addition treatments. Methods We established a manipulative experiment with altered litter input and nitrogen addition treatments in a semiarid typical grassland in West Ujimqin Banner, Inner Mongolia. A randomized block split-plot design was applied with five blocks. Three litter input treatments, including litter removal (C0), control (C1) and litter addition (C2), were assigned randomly in each block. Each plot (6 m × 7 m) with altered litter input treatment was separated into two subplots. One of the subplots was assigned as the N addition treatment (N1) and another subplot was considered as the control treatment without N addition (N0). In N addition treatment, 15 g N·m–2·a–1 N fertilizer (as NH4NO3) was applied every year since 2013. Aboveground primary productivity (ANPP) in community and plant functional group levels of each treatment were determined during the peak season from 2013-2018. Important findings Based on 6-year measurements, we found: 1) Increased litter input and nitrogen addition increased community aboveground net primary productivity (ANPP). Compared with the control, litter removal treatment significantly decreased ANPP by 8.4% and 7.6% without and with N addition, respectively; while enhanced ANPP by 10.7% and 6.3% without and with N addition, respectively. 2) Different responses of plant functional groups to altered litter input and N addition led to a change in plant functional group composition. The biomass of perennial bunchgrass (PB) and perennial rhizome grass (PR) increased significantly with the increment of litter and nitrogen, which enhanced their dominant status in the community. 3) Improved soil water condition by litter input and nutrient supply by N addition are the major pathway which enhanced by litter and N addition, because of the improved soil water and nutrient supply. These results show that proper management, such as grazing exclusion and reducing grazing intensity, can promote productivity by increasing inputs of litter in semiarid grasslands, which leads to the maintenance of ecosystem stability. Suitable nutrients management, like nitrogen addition, is also helpful for productivity improvement and its recovery of degraded grasslands.

Variation and correlation in functional traits of main woody plants in Cyclobalanopsis glauca community in karst hills of Guilin, southwest China

2020-07-09 00:00:00.0

Aims Exploring the variation and the relationship between different functional traits of different growth forms and life forms woody species is helpful to understand the adaptation strategies of plants to the external environment, which is of great significance for an understanding of community assembly and biodiversity maintenance mechanisms. Methods We investigated and measured the leaf chlorophyll content (CHL), leaf thickness (LTH), leaf area (LA), leaf dry weight (LDW), specific leaf area (SLA), leaf dry matter content (LDMC), leaf tissue density (LTD), twig dry matter content (TDMC) and twig tissue density (TTD) of 18 main woody species from Cyclobalanopsis glauca community in karst hills of Guilin, southwest China. Traits variation among different plant functional types (growth form and life form) were further analyzed by a series of methods, such as one-way analysis of variance (One-way ANOVA), and linear mixed-effects model. In addition, the relationships between 9 functional traits on individual and species levels were assessed by Pearson’ s correlation test and principal component analysis (PCA). Important findings The results showed that: (1) The 9 functional traits had different degrees of variation. Specifically, LA and LDW had the maximum coefficient of intraspecific and interspecific variation, while the intraspecific and interspecific variation coefficient of TDMC and TTD was the smallest. (2) For different growth forms, there were significant differences in most functional traits between trees, shrubs and woody lianas. (3) For different life forms, except that the deciduous species showed significantly higher LA and SLA value than evergreen species, the other 7 functional traits were evergreen species significantly higher than those of deciduous species. (4) There were differences in the intraspecific and interspecific variation of functional traits between different life forms and growth types plants. Except for some plant functional traits showed the intraspecific variation higher than interspecific variation, most of the other functional traits showed the interspecific variation was basically higher than intraspecific variation. (5) The relationship between 9 functional traits is roughly the same at the individual level and the species level, while the significant correlation ratio at the individual level is higher than the species level. In conclusion, the interspecific variation of plant functional traits is basically higher than the intraspecific variation, but the intraspecific variation cannot be ignored. In addition, different growth form and life form species adopt different ecological strategies to adapt to the karst habitat. Future research should be based on sampling at the individual level, and in combination with environmental factors to explore the variation and correlation in functional traits of different plant functional types at different scales.

Analysis of vegetation index changes and driving forces in inland arid areas based on random forest model: a case study of the middle part of Northern slope of north Tianshan Mountains

2020-07-07 00:00:00.0

Aims Vegetation changes in arid areas in the context of global change are both affected by climate change and human activities. Quantitative evaluation of vegetation change characteristics and their driving mechanism is of great significance for monitoring the ecological environment change in arid areas and promoting the sustainable development of the region. Due to complexity and diversity human activities are difficult to quantify, some researches are mostly limited to the response of NDVI to climate change, and the impact of human activities has not been considered sufficiently, which has led to biases and uncertainties. Methods Firstly, this paper proposes a method for quantifying human activities related to land use types. Then the contribution of climate change and specific human activities to the NDVI in the middle part of Northern slope of north Tianshan Mountains was analyzed by using multiple linear regression model and random forest model. Important findings An overall upward trend was observed in NDVI variations from 2000 to 2015. The fitting accuracy of NDVI based on random forest model was significantly better than multiple linear regression model, and its R2 improved by at least 24%. The contribution of human activities related to arable land to NDVI change in the middle part of Northern slope of north Tianshan Mountains showed an increasing trend during study period and was greater than climate factors from 2000 to 2015.This study provides new ideas for the study of the effects of climate change and human activities on vegetation, as well as scientific basis for the protection and restoration of ecological environment in arid areas.

NDVI dynamic of Ecological Function Protected Zone its climatic factors driving

Aijuan LI Xiaohua Xu Xiancheng Yang Qiangqiang Yang — 2020-07-07 00:00:00.0

Aims It is very important to study the Normalized Difference Vegetation Index (NDVI) change and its response to climate factors for understanding the dynamic the Ecological Functional Protected Zone (EFPZ) under the climate warming. Methods Based on the MODIS NDVI data of the growing season (April-October) from 2000 to 2015, Using two spatial scales of EFPZ subarea and pixel, the dynamic of NDVI and the correlation between NDVI and climatic factors in 46 EFPZ was analyzed by linear tendency and partial correlation method. Based on the significant level of partial and multiple correlations between NDVI and precipitation, temperature factors, the regionalization of vegetation dynamics driven by climatic factors was carried out. Important findings (1) The NDVI of EFPZ showed an increasing trend, with the average linear slope of 0.045/a. Pixel scale analysis showed that NDVI increased significantly were mainly in the central and the northeast. (2) The partial correlation coefficients between NDVI and precipitation in EFPZ ranged from -0.30 to 0.72, and 32 subareas were positively correlated. The partial correlation between NDVI and air temperature ranged from - 0.36 to 0.92, and 39 subareas were positively correlated. The analysis of pixel scale shows that 50.6% of the pixel NDVI is positively correlated with precipitation, mainly distributed in Northeast and Northwest China. In addi-tion, 64.6% of the pixels NDVI were positively correlated with temperature, mainly distributed in northeastern and the northern edge of the Qinghai-Tibet Plateau. (3) Temperature-precipitation strong driving type is the main driving type, accounting for 38.7% of the total area. Temperature driving type is the secondary driving type, accounting for 27.3%. Non-climatic driving type accounts for 17.6%.

Vertical variation and economic strategy of leaf trait of major tree species in a typical mixed broadleaved-Korean pine forest

Xun Yanhan Xueying Di Guang-Ze JIN — 2020-07-07 00:00:00.0

Aims An analysis of the variations in leaf traits of different tree species contributes to the understanding of plant community structures. Methods This study explored the effect of the light environment on leaf traits at different canopy heights in a typical mixed broadleaved-Korean pine forest. We measured the leaf mass per area (LMA), leaf thickness (LT), leaf dry matter content (LDMC), chlorophyll content (CCI), leaf carbon content (C), mass-based and area-based nitrogen content (Nmass and Narea), and mass-based and area-based phosphorus content (Pmass and Parea) for 15 broad-leaved tree species in a typical mixed broadleaved-Korean pine forest. Important findings We found that the LMA of Fraxinus mandschurica and Populus ussuriensis in the upper canopy were significantly higher than that in the lower canopy, but no significant changes were detected in other species within the canopy. The CCI of Betula platyphylla increased from the lower to upper canopy. In contrast, the CCI of Ulmus japonica in the upper canopy was significantly higher than that in the middle canopy. The Nmass of Fraxinus mandschurica in the middle canopy was significantly higher than that in the upper canopy. These results indicated that the variations in leaf traits within the canopy among species were different. The LMA was positively correlated with the LT and LDMC in all three canopies, but the correlations of other trait combinations were only significant in one or two canopies. The results suggested that the leaves of Populus davidiana and Populus ussuriensis tended to adopt survival strategies involving lower photosynthetic ability, nutrient concentrations, and respiratory rates; the leaves of Phellodendron amurense and Maackia amurensis tended to be located at the other end of the economics spectrum with contrasting trait values. Differences in the response to light among tree species may alter leaf morphological and chemical traits in canopy layers, thus contributing to community assembly and species coexistence.

Effects of plant interspecific interaction and warming on soil microbial community in root zone soil of two dominant tree species in the subalpine coniferous forest in southwestern China

Liang Jin tao enwang Jun HU HE He-Liang — 2020-07-03 00:00:00.0

Aims Soil microbial community composition and structure were regulated by temperature and plant species. Picea asperata and Abies faxoniana were planted in the mono plantations, and always inter-cropping in the natural forests of the subalpine region in southwestern China. However, the effects the two species and their interaction on soil microbial community under future climate warming remain unclear. Methods An experiment was conducted to examine the effects of warming and plant species on soil microbial community composition with two levels of temperature (unwarmed and warmed with infrared heater) and four planting patterns (single A. faxoniana, single P. asperata, A. faxoniana mixed P. asperata, and bare land). Root zone soil of different treatments were sampled to estimating the microbial biomass and microbial community composition by phospholipid fatty acid (PLFA) analysis. Important findings The results indicated that: (1) Both P. asperata and A. faxoniana mono-planting significantly increased the main soil microbial groups and the total PLFAs contents, regardless of warming. But the PLFAs content was only increased by mixed planting in unwarming plot. On the other hand, warming was helpful for fungi (F) in unplanted plots and gram-negative bacteria (GN) in the P. asperata plots, respectively. However, warming significantly decreased soil microbial biomass in A. faxoniana and the mixed planting plots. (2) Principal component analysis (PCA) showed that effects of planting P. asperata and A. faxoniana on soil microbial community composition were greater under unwarming condition. All the planting treatments significantly decreased the ratio of gram-positive/gram-negative bacteria (GP/GN) and increased the ratio of fungi/bacteria (F/Bac) in unwarmed plots. However, significant effects on GP/GN and F/Bac ratios were only observed in A. faxoniana plots under warming condition. (3) PLFAs contents were positively correlated with soil carbon content, and F/Bac ratio was significantly correlated with soil pH and inorganic N. These results showed the effects of warming on soil microbial biomass and composition varied among the tree species. While the effects of P. asperata and A. faxoniana were weakened under warming condition. Our results provided a vital theoretical basis for further studying on the responses of soil microbial communities to vegetation and global climate change in the studied zone.

Biotic interactions and ecosystem dynamics under global change: From theory to application

2020-07-03 00:00:00.0

Under intensifying human activities and climate change, spatiotemporal changes in ecosystem composition and structure are becoming increasingly drastic and intricate, and there are trends of degradation in many ecosystems. Thus, an improved understanding of ecosystem dynamics and their underlying mechanisms in the context of global change can not only help resolve fundamental theoretical questions in ecology, but is also critical to applied issues in ecosystem restoration and conservation. Overviewing different models of ecosystem dynamics (gradual continuum, threshold/regime shift, and stochastic), we first conceptualized the mechanisms by which biotic interactions can potentially modulate ecosystem dynamics. Then, we reviewed the state of the art in the study of how biotic interactions regulate secondary succession, regime shift, and species range shift—ecosystem dynamics subject to intense recent investigation. We further discussed studies that tested application of biotic interactions in ecosystem restoration and conservation. A growing body of research has shown 1) that multiple types of biotic interactions, such as competition, promotion (including mutualism), and trophic interactions, can drive or substantially alter the patterns, directions, and rates of ecosystem change at various spatiotemporal scales, and 2) that managing biotic interactions is likely to greatly amplify success of ecosystem restoration and conservation. To move forward, we highlight that further research is needed to better understand how the impacts of biotic interactions on ecosystem dynamics vary spatially and temporally, how biotic interactions modulate ecosystem dynamics under multiple anthropogenic disturbances, and how best to manage biotic interactions to optimize ecosystem conservation and restoration.

Characteristics of soil enzyme activites and stoichiometry and its influencing factors in Sharp-tooth oak forests in the Qinling Mountains

2020-07-03 00:00:00.0

Aims The dynamic changes and driving factors of soil enzyme activities and stoichiometry in the micro elevation gradient is of great significance in the study of nutrient cycling process in ecosystem. Methods In the present study, the Quercus aliena var. acuteserrata forest belts at the elevation of 1308, 1403, 1503, 1603, 1694 and 1803 m in Taibai Mountain were sampled to determine the contents of carbon (C), nitrogen (N), and phosphorus (P) in leaves, litters, roots and soils, and the activities of Alkaline phosphatase, β-1,4-glucosidase, Cellobiohydrolase, β-1,4-xylosidase and β-1,4-N-acetylglucosaminidase. Important findings Our results showed that the altitude gradient had a great impact on the activities of five soil enzymes. CBH and βG increased first and then decreased with the altitude, while βX was the opposite. The NAG and AKP activity showed a downward trend at 1408–1694 m and increased at 1803 m. The total enzyme activity index exhibited a decreasing trend along the altitudes. The correlation analysis results indicated that soil enzyme activity and its stoichiometric ratio were controlled by plant, soil C, N, P resources, and soil water and heat conditions. The high correlation of SOC could be the main factor affecting the change of soil enzyme activities in the Quercus aliena var. acuteserrata forest. In short, the soil enzyme activities and stoichiometry were different in the micro-scale elevation gradient, affected by the C, N, and P resources of plant and soil. This study not only provides a scientific reference for the biogeochemical cycling process of elements in this region, but also contributes to the understanding of soil enzyme stoichiometry and its driving mechanism in the micro elevation scale, which has a positive implication for climate change impact projections.

Effects of chicken manure addition on the functional properties of Melilotus officinalis growing in the degraded grassland

2020-07-03 00:00:00.0

Aim Nutrient deficiency is one of the important factors that cause grassland ecosystem degradation. Nutrient addition was regarded as an effective method to restore the degraded grassland. Legume, an important plant population of grassland ecosystem, would be significantly affected if adding nutrient into the ecosystem. This study aims to clarify the effects of nutrient addition on the functional traits of legume. Methods We carried out a chicken manure adding gradient (CMA, L0 –– L6 were 0, 500, 1000, 1500, 2000, 2500 and 3000 kg·hm-2·a-1) control experiment in Onqin Daga Sandy Land, with Melilotus officinalis, a typical legume plant, as our object. Important findings The results showed that the leaf nitrogen (N), phosphorus (P), potassium (K) content, maximum photosynthetic rate (Pnmax), water use efficiency (WUE), specific leaf area (SLA) and plant height (H) of M. officinalis were significantly affected by CMA. Leaf N, P and K content of M. officinalis increased linearly with the increase of CMA. When CMA amount arrived at 3000 kg·hm-2·a-1 (L6), the increasing range of leaf N, P, and K content of M. officinalis was 15%, 67% and 25% respectively compared with L0. CMA also influenced H, SLA, Pnmax and WUE of M. officinalis, showing a trend of increasing first and then decreasing. When CMA amount was lower than 1500 kg·hm-2·a-1 (L3), H, SLA, Pnmax and WUE of M. officinalis increased significantly, with the range of 51.1%, 18.2%, 11.7% and 38.1% respectively in August; then they all decreased significantly; there was no significant difference between L6 and L0. CMA in an appropriate amount could improve the photosynthetic capacity and water use capacity of legumes growing in grassland, and then promote their growth, ultimately make for the maintenance of their population.

Study on the hydraulic lift of Medicago sativa and Astragalus laxmannii and its effect on their neighbor plants

Lin Zhu Tiantian Wang Xuelin Zhao Xing Xu — 2020-07-03 00:00:00.0

Aims A variety of plant species can release soil water which is absorbed from wet soil layers to the dry soil layers during the period when transpiration rate is low (hydraulic lift). The purpose of this study is to explore the “so-called” hydraulic lift phenomenon for the mixed sowing combinations of two leguminous forages Medicago sativa and Astragalus laxmannii leguminous with gramineous forages respectively, uncovering the inter-specific relationship between forages with deep and shallow roots and providing theoretical basis for the establishment of mixed grassland. Methods A split-root pot experiment was conducted outdoors. Two leguminous forages Medicago sativa and Astragalus laxmannii were sowed individually or sowed with a gramineous forage (Secale cereal ‘Dongmu 70’) with proportion of 3:7, 5:5 and 7:3. While the soil water content was measured continuously, deuteroxide (D2O, D% > 99.9%) tracing technique was adopted to test the occurrence of hydraulic lift or not and to calculate the lift water quantity. Important findings The yield of Secale Cereal ‘Dongmu 70’ in mixed sowing with Astragalus laxmannii was higher than that with Medicago sativa. The yield of AC2 (Medicago sativa: gramineae being 5:5) and BC3 (Astragalus laxmannii:gramineae being 7:3) were was higher than other mixed sowing proportions in a same mixed sowing combination. There was significant difference in the average daily water lift during the whole growth period among different single sowing or mixed sowing combinations. The lift water amount for a given leguminous forage was higher in mixed sowing combinations than in single sowing combinations. Astragalus laxmannii displayed higher daily water lift quantity regardless of single sowing or mixed sowing. The average daily water lift or BC2 (Astragalus laxmannii:gramineae being 5:5) was significantly higher than other combinations. δD of soil water in upper and bottom pots significantly increased after treated with deuteroxide tracer. The values of soil water δD in the upper pot, xylem water δD, whole plant Δ13C and yield of Secale cereal ‘Dongmu 70’ have provided the evidence that the water status or yielding performance of Secale cereal ‘Dongmu 70’ in the combinations of BC1 (Astragalus laxmannii:gramineae being 3:7) and AC2 was better than other mixed combinations. This study validated the hypothesis that the phenomenon of hydraulic lift occurred when the deep-rooting leguminous and gramineous forages with shallow root were sown together. The water lift by the tested leguminous forages has been absorbed by their neighbor plants gramineous forage.

Variation in biomass allocation of Nitraria tangutorum during different phenological phase

Lei XING Qing-He LI Hui-Qing Li Gaojie SUN — 2020-07-03 00:00:00.0

Aims The pattern of plant biomass allocation represented the plant's response to the environment and is accompanied by every stage of plant life history. So it is closely related to the growth and development of plants. There have been reports on the size dependence of plant biomass allocation, but few studies have reported on its responses to different phenological phase. Methods In this study, Nitraria tangutorum in Ulan Buh Desert was used as the research object. The biomass of different organs (root, layering, shoot, branch, leaf and reproductive organ) in the flowering, fruiting and vegetative growth stages in two consecutive years of 2016 and 2017 were measured. The significant comparison of slope and intercept of the fitted equation with Standardized-major-axis were respectively used to discuss the variation of size dependence and the biomass allocation in different phenological phase or ages, especially between the aboveground and underground biomass and between the support and assimilation organs. Important findings The results showed that the effect of reproductive allocation on biomass allocation pattern of N. tangutorum is mainly reflected in the scale of relative biomass allocation (36.00%) rather than the extent of size dependence (16.67%). The reproductive growth has a greater impact on the biomass allocation pattern of new stems, which changes the size dependence extent among different phenological phases, but the trend is inconsistent. The reproductive growth increases the scale of relative biomass allocation to leaves and reduces it to older stems, but did not change their extent of size dependence. The biomass allocation rate in the underground part of N. tangutorum will increase with the accumulation of its biomass, but the reproductive allocation can slightly decrease this rate. N. tangutorum have a higher rate of biomass allocation to supporting organs as the biomass of the plant increases, but over time, it is more likely to allocate biomass to assimilating organs.

Uptake kinetics of nitrogen and phosphorus by Zostera marina

Shiq-Qi Li Yanhao Zhang Zheng Li Peidong Zhang — 2020-07-02 00:00:00.0

Aims Nutrient availability is an external factor that affect the growth of seagrasses. However, the demand for and absorption of different forms of nitrogen and phosphorus by different tissues of seagrasses are unclear. In this study, the uptake of nitrogen and phosphorus by Zostera marina was studied to determine the nutrient uptake kinetics. The objectives of this research are to: 1) investigate the absorption characteristics of ammonia nitrogen, nitrate nitrogen and phosphate in Z. marina; 2) evaluate the differences in absorption between the different forms of nitrogen; and 3) analyses the differences in absorption between the different tissues of Z. marina. Methods Equipment was used to separate the aboveground and belowground tissues of Z. marina. Six concentration levels of ammonia nitrogen, nitrate nitrogen and phosphate were established to experimentally test the uptake kinetics of nutrients by Z. marina. The nutrient concentrations in different parts of seawater column were measured to determine the nutrient changes and calculate the kinetic characteristics of nutrient uptake. Important findings 1) The absorption of ammonia nitrogen, nitrate nitrogen and phosphate by Z. marina was consistent with the characteristics of saturated absorption kinetics. The relationship between the absorption rate and the nutrient concentrations in water could be described by the Michaelis-Menten equation. 2) The maximum absorption rate (Vmax) of ammonia nitrogen by Z. marina (52 μmol·g-1·h-1) was significantly higher than that of nitrate nitrogen (39 μmol·g-1·h-1). 3) Both aboveground and belowground tissues of Z. marina could absorb nutrient, but the Vmax of leaves (aboveground tissues) for ammonia nitrogen, nitrate nitrogen and phosphate absorption were 43.1, 30.5 and 15.6 μmol·g-1·h-1, respectively, which were 2.6-fold, 1.2-fold and 6-fold higher than the corresponding Vmax of belowground tissues. The results show that the absorption capacity of Z. marina for ammonia nitrogen is higher than that for nitrate nitrogen, and the absorption of nitrogen and phosphorus may depend primarily on the aboveground tissues (leaves). The results provide a theoretical basis for the study of the mechanisms of nitrogen and phosphorus uptake and utilization by Z. marina and the evaluation of marine ecological impacts.

Seed predation and dispersal pattern of Fagaceae species in a fragmented landscape, eastern China

Yuchen Zhong Bin Wang Zhongping Fang Xiaozhong Xu Ming-Jian YU — 2020-06-23 00:00:00.0

Aims Due to the area effect and edge effect, habitat fragmentation can alter competition intensity, foraging behavior and shelter condition of scatter-hoarders, and consequently affect seed predation and dispersal patterns. Though there have been some studies focusing on seed dispersal in fragmented landscapes, few studies have compared the effects of habitat fragmentation on seed predation and dispersal among multiple species. Methods To explore how species identity, abundance of scatter-hoarders, seed production, island size and edge effect work together to influence seed fates and dispersal distance, we conducted seed predation and dispersal experiments for six Fagaceae species in the island and mainland forests of the Thousand Island Lake region in Zhejiang Province, eastern China. Important findings (1) There were significant differences in seed fates and dispersal distance among six Fagaceae species. (2) Seeds were removed faster on the islands than on the mainland, and even faster on smaller islands than on larger islands. Further, seeds were removed faster at the island edges than in the interiors. (3) There was a significant interactive effect between island size and species identity on the probability of seeds eaten in situ. More seeds of Quercus fabri were eaten in situ on larger islands. (4) Seeds had the highest probability of removal on small islands; the relative abundance of scatter-hoarders had a negative effect on the probability of seeds cached. These findings implied that habitat fragmentation altered seed predation and dispersal patterns, and that area effect posed species-specific effects on seed predation and dispersal patterns, which would contribute to forest regeneration and biodiversity maintenance.

Nitrogen-fixing Bacteria Alleviates the Nutrient Competition between Arbuscular Mycorrhizal Fungi and Solidago canadensis under Nitrogen Limited Environment

Fang Pang Wei-Kang Xia Min He Shan-Shan Qi DAI Zhicong DU Dao-Lin — 2020-06-23 00:00:00.0

Aims The prerequisite for arbuscular mycorrhizal fungi to form a symbiotic relationship with host plants is nutrient-rich. We hypothesized that the arbuscular mycorrhizal fungi (AMF) will pose nutrient competition with host plants in an extremely nitrogen-constrained environment, the intervention of nitrogen-fixing bacteria will alleviate this situation. Methods In order to verify our hypothesis, we designed and found the concentration of nitrogen which caused Solidago canadensis’ growth restriction, then the relationships among AMF, S. canadensis and nitrogen-fixing bacteria were investigated. Important findings The results showed that AMF could not form a good symbiotic relationship with S. canadensis under the nitrogen-restricted environment, and nitrogen restriction would motivate S. canadensis to optimize the biomass allocation strategy, increased the underground biomass and reduced the colonization rate of AMF, indicating that the competition relationship exists between AMF and S. canadensis under nitrogen-restricted. However, with the addition of nitrogen-fixing bacteria, the colonization rate of AMF and biomass indicators of S. canadensis promoted. These findings indicated that nitrogen-fixing bacteria could moderate the nitrogen competition between AMF and S. canadensis under the condition of nitrogen restriction. This study deepens our understanding of the invasion mechanism of alien plants interacting with a variety of microorganisms in complex environments.

Bryophyte societies on the fallen logs of Pinus armandii with different decay class in Sygera Mountains

Ling ZHANG Ying-Jie FAN Xiao-Tong SONG Min Li Xiaoming Shao Xiao-Rui WANG — 2020-06-12 00:00:00.0

Aims Fallen logs play important roles in maintaining the health and the renewal of forest ecosystem, but the difference of bryophyte societies with different decay class on fallen logs is unclear. Methods To understand the regularity and influencing factors of these changes, we investigated the bryophytes with quadrats along the trunks on 4 fallen logs of Pinus armandii with different decay class at the same site in Sygera Mountains, Tibet, then, the measured data were collected and analyzed. Important findings There were 22 families and 52 species of bryophytes developing on 4 fallen logs, including 13 families and 38 species of Musci, 9 families and 14 species of Hepaticae. According to the characteristics of the co-owned dominant species, 14 societies were obtained. With the increasing of decay class of fallen logs, which matrix and surrounding environment constantly change, the bryophyte diversity increased gradually, while the number of societies and the total bryophyte coverage fluctuated continuously. Bryophyte species varied from drought-tolerant tall turfs, such as Orthotrichaceae and Leucobryaceae to fast-growing cushions or mats in humid and shady environments, such as Mniaceae, Thuidiaceae and Brachytheciaceae. The complexity of bryophytic society spatial structure increased gradually. Fallen logs are important growth substrates for a variety of bryo-phytes. Bryophyte societies on it vary with decay class, moisture and light conditions.

A review on the effects of nitrogen and phosphorus addition on tree growth and productivity in forest ecosystems

Jiguang Feng — 2020-06-12 00:00:00.0

Nitrogen (N) and phosphorus (P) inputs induced by anthropogenic activities and atmospheric N and P deposition have largely increased the availability of soil N and P in terrestrial ecosystems, which have considerably affected terrestrial carbon cycling processes. Tree growth and productivity in forest ecosystems play an important role in global carbon cycling, and determine the magnitude and direction of terrestrial carbon sequestration. Currently, a large number of field manipulation experiments have been conducted to investigate the effects of N and/or P addition on tree growth, but the results from these studies were inconsistent. Such inconsistent results might be affected by multiple factors, including biological, environmental and experimental variables. Here, we reviewed the present research status of the effects of N and P addition on tree growth and productivity in forest ecosystems based on three aspects, including the number of publications and experiments with field N and P addition, and the global distributions of these experiments. Then, we summarized the methods for assessing tree growth and productivity at ecosystem level in forest ecosystems, including relative growth rate and absolute increment. According to the related results, we reviewed the regulating factors that affect tree growth and productivity, and the potential mechanisms for such factors, including climate, tree size and stand age, plant functional traits (including type of tree-associated mycorrhizal fungi, N-fixation property of trees, and conservative and acquisitive functional traits), plant-microbe interaction, ambient nutrient (i.e., N and P) deposition rate, and experimental variables. Finally, we summarized the current studies, and pointed out five aspects that are urgently needed to provide further insights in future studies, including the physiological mechanism of how tree growth responds to N and P addition, the tradeoff and allocation among growth of various parts of tree under N and P addition, the role of plant functional traits in regulating and predicting the responses of tree growth to N and P addition, how the competition among trees regulates the responses of tree growth to N and P addition, and conducting long-term and coordinated distributed field experiments investigating the effects of N and P addition on tree growth and forest productivity at the global scale.

Shrub traits of forest and shrubland reveal different life strategies

2020-06-12 00:00:00.0

Aims Shrub plants play important roles in both forest and shrubland ecosystems. This study aims to explore the adaptation strategies of shrubs in different habitats by analyzing the differences of functional traits of shrubs grown in understory of forest communities and in two shrublands. Methods Nine functional traits of leaves and twigs collected from the dominant shrub plants in 24 plots distributed in three habitats: forest shrub layers, secondary shrubland and primary shrubland, in Beishan Mountain of Jinhua, Zhejiang Province, were measured. The overall differences, inter- and intra-specific variations and the differences in various life forms of shrub traits in three different habitats were statistically analyzed. Important findings Results show that: 1) There are differences of nine plant traits for shrubs grown in three different habitats. The understory shrubs have larger leaf area (LA) and specific leaf area (SLA), smaller leaf dry-matter content (LDMC), leaf tissue density (LTD) and twig tissue density (TTD), while shrubs in secondary shrubland have larger leaf thickness (LT) and LTD, smaller SLA and twig dry-matter content (TDMC) compared with shrubs from the primary shrubland. 2) The inter- and intra-specific variation coefficients of SLA, twig diameter (TD), TTD, and TDMC in understory shrubs are the largest, while the inter- and intra-specific variation coefficients of SLA, LDMC, TDMC, and TTD in secondary shrubland are the smallest. 3) Among different life forms, the understory evergreen shrubs have significant higher LT, LTD, and LDMC than deciduous shrubs, while deciduous shrubs have significant higher SLA than evergreen shrubs. The differences of LT and SLA between evergreen and deciduous shrubs of primary shrubland are the same as those of understory shrubs, but the differences of LTD and LDMC between evergreen and deciduous shrubs have the opposite trend. 4) The main source affecting shrub traits are species and theinteraction between species and habitat. In short, compared to shrubs from shrublands, understory shrubs in forest communities form a series of trait combinations that are larger LA and SLA, smaller LTD, TTD and LDMC to grow faster to adapt to the understory environment with less light and stronger competition. This is a quick investment-return (resource acquisitive) strategy. Secondary shrubland and primary shrubland have a series of shrub trait combinations that are larger LT, LTD, LDMC and TTD, smaller LA, SLA to store more nutrients and grow slower. This is a slow investment-return (resource conservative) strategy. Different combinations of shrub functional traits and their various life strategies can provide guidance to the ecological restoration of degraded vegetation in the subtropical region of China.

Estimation on seasonal dynamics of alpine grassland aboveground biomass using phenology camera-derived NDVI

Zhe Chen Hao WANG Jinzhou Wang Huijin Shi Jin-Sheng HE — 2020-06-12 00:00:00.0

Abstract Aims Accurate assessment of plant aboveground biomass is important for optimizing grassland resource management and for understanding the balance of carbon, water and energy fluxes in grassland ecosystems. This study constructed the optimal empirical models by near-surface remote sensing NDVI data, and then estimated plant aboveground biomass in an alpine grassland on the Qinghai-Xizang Plateau. Methods Using the dataset of both the field-measured aboveground biomass and the NDVIRS observed by plant canopy spectrometer (RapidSCAN), we constructed the empirical models for estimating aboveground biomass in different phases of the growing season across 2018 and 2019. Using the NDVICam time series observed by phenology camera and the estimated models, we simulated seasonal dynamics of aboveground biomass in 2018. Important findings (1) The seasonal dynamics of NDVICam, NDVIRS and aboveground biomass exhibited a similar unimodal pattern; however, the timing of peak NDVI value (August) preceded that of peak aboveground biomass (July). (2) The best model for estimating aboveground biomass is the power function in May, July and September, and the quadratic equation in June and August. The estimation accuracy ranged from 0.29 to 0.77. (3) The estimation of aboveground biomass based on the models in different phases of growing season (R2 = 0.91) showed a higher accuracy compared to that based on the model at a single time (September)(R2 = 0.49). Our results suggest that the near-surface remote sensing is an effective approach for estimating alpine grassland aboveground biomass, and further investigation on the seasonal growth of plants will help accurately evaluate grassland resources.

Effects of drought stress on photosynthesis, growth and root structure of transgenic PtPIP2;8 poplar 84K (Populus alba × P. glandulosa)

Jin-Xia FENG LIU WENXIN Xian-Chong WAN — 2020-06-12 00:00:00.0

Aims In this study, transgenic poplar 84K (Populus alba × P. glandulosa) seedlings with different expression levels of aquaporin gene (PtPIP2;8) were used to test changes in growth, photosynthesis and root structure. The function of aquaporin gene PtPIP2;8 and its response to drought stress were analyzed to provide reference for transgenic breeding to obtain poplar variaties with strong drought tolerance. Methods We selected PtPIP2;8 silencing line of poplar 84K, PtPIP2;8 overexpressing line of poplar 84K and wild type (WT) as the research object. The Real-time fluorescence quantitative PCR technique was used to detect the PtPIP2;8 expression in roots, stems and leaves. Root hydraulic conductance was measured by high pressure liquid flow meter. The photosynthetic light-response curve, and gas exchange parameters were measured by a Li-6400 photosynthetic system. Growth indexes were determined, and the root length, root surface area, root volume and total root tips were scanned and then analyzed with the root analysis software. Important findings The results showed this gene in the wild type was mainly expressed in the root system. Transgenic plants with overexpression of this gene had significant expression in roots, as well as in stems and leaves. The transgenic plants with inhibited expression had only a small amount of expression in the root, and the expression level were 1/20 and 1/80 of wild-type and overexpression line, respectively. The root structure analysis showed that the total root length, total root surface area, total root volume and total root tips of overexpression line were significantly lower than RNAi-silence line and WT, but root hydraulic conductance was significantly higher than RNAi-silence line and WT. The results showed that the aquaporin gene PtPIP2;8 participated in plant water transport and improved water transport efficiency. Under normal water conditions, the height and leaf area of RNAi-silence line were significantly lower than overexpression line and WT, and the root-shoot ratio was significantly higher than overexpression lines and WT. After drought stress, the net photosynthetic rate (Pn) and stomatal conductance (Gs) of RNAi-silence line decreased slightly , maintaining a relatively high Pn. Diurnal changes of Pn and Gs in RNAi-silence lines had single-peak type, which was the decrease of photosynthesis caused by stomatal limitation. Diurnal changes of Pn in overexpression lines and WT had two-peak type, indicating the effects of non-stomatal limitation on photosynthesis. After drought stress, Pn of RNAi-silence line decreased very little, while overexpression line and WT decreased significantly, especially at 13 and 15 points, indicating that overexpression line and WT were more sensitive to drought stress and had greater influence from drought compared with the RNAi-silence line. Under drought stress, the relative growth rate and total biomass of RNAi-silence line decreased the least, and the root-shoot ratio was the highest. The total root surface area, total root volume and total root tips of RNAi-silence line were significantly higher than WT. The results show that aquaporin gene PtPIP2;8 directly participates in the water transport, which can improve the water transport efficiency. And aquaporin PtPIP2;8 gene transformation affects root development and growth of plants. The decrease of root development and the increase of leaf area of overexpression line weaken its drought resistance, while RNAi-silence line increases its drought resistance with reduced leaf area, increased root growth and root-shoot ratio. According to the results of this study, the non-aquaporin water-conducting mechanism has greater tolerance to drought, while both the wild type and overexpression line are more sensitive to drought, especially overexpression line.

Research progresses of plant-herbivore interactions

Zhong Zhiwei Xiaofei Li De-Li WANG — 2020-06-12 00:00:00.0

Plant-herbivore interaction is one of the most common and important interspecific relationships in nature, which is the core and foundation of the food web theory. In this paper, we review the effects of herbivores on the characteristics of plant individual, population and community, as well as the defense strategies and mechanisms of plants against herbivores at the levels of individual, population and community. Herbivory can significantly change the growth, reproduction and survival rate of plant individuals and populations, which can in turn affect the composition and diversity of plant communities. In order to defend against herbivory, plants have evolved a series of defense mechanisms at individual, population and community levels. At individual and population levels, plants avoid herbivory mainly by chemical and physical defense. At community level, however, plant defenses achieved mainly by their influences on the behaviors of herbivores. This paper then introduces and compares important hypotheses and theories in related fields. Finally, we point out major existing research issues and identify possible future research directions. Given that natural systems are experiencing strong disturbances from human activities and climate changes, exploring how these disturbances affect plant-animal interactions, and how these changes in plant-animal interactions feedback on the structure, function and stability of the ecosystem, will not only has important theoretical significance, but also help us to formulate successful ecosystem management policy in the future.

Predicting phenology shifts of herbaceous plants on the Tibetan Plateau under climate warming with the space-for-time method

LI XUEYING PEIXIAN LI ZHIYING XIE CENLIANG ZHAO — 2020-06-08 00:00:00.0

Aims To analyse the feasibility of space-for-time method in predicting phenology shifts of Plantago asiatica and Taraxacum mongolicum on the Tibetan Plateau, as well as revealing the phenological changes of the two herbaceous plants under climate warming. Methods The observed phenological data for Plantago asiatica and Taraxacum mongolicum from 10 sites on Tibetan Plateau during 2002–2011, as well as the meteorological data (i.e., daily mean air temperature) were collected. First, multiple linear regression models were bulit between geographic factors (longtitude, latitude and altitude) and phenological events/annual mean temperature at different altitude gradients. Then, the longtitude and latitude were kept to be unchanged, and the unary linear regression models between phenological events/annual mean temperature and altitude were built. Finally, the altitude was used as the “bridge” to indicate the relationship between the change of phenological events and the change of annual mean temperature. Important findings The temperature decreased with the increasing altitude (R2 > 0.89, p < 0.05), illustrating that changes of altitude gradients can be used to substitute for changes of annual mean temperature. The change in the simulated phenological events of the two herbaceous plants all showed a strong dependence on the change of altitude (R2 > 0.70, p < 0.05), which contributed the most among the geographic factors. Strong dependences were observed between the simulated phenological events and the simulated annual mean temperature (R2 > 0.93, p < 0.05), showing that phenological events could be predicted by the annual mean temperature with the space-for-time method. For Plantago asiatica, the first leaf date (FLD) and the first flowering date (FFD) occurred earlier with increasing annual mean temperature as 5.12 and 5.40 days per ℃, respectively, while the common leaf coloring date (LCD) occurred later as 4.81 days per ℃. The FLD and FFD of Taraxacum mongolicum advanced by 6.50 days and 7.76 days per ℃ of increase in the mean annual tem-perature while the LCD delayed by 6.70 days per ℃.

Characteristics and influencing factors of Bowen ratio variation in typical terrestrial ecosystems in China

Song-Yu HUANG Xin JIA Jia-Jia ZHENG Rui-Zhi YANG Yu MU He-Di YUAN — 2020-06-08 00:00:00.0

Background Bowen ratio(β) is an important parameter in land-surface process, which affects the energy exchange between the surface and the atmosphere, a clear understanding of the spatial variation and influencing factors of β can help predict the relationship between surface energy balance and climate. Methods We collected the published literature on the measurement of surface energy balance by the EC method (Eddy Covariance) carried out in different ecosystem types in China, constructed the database of Bowen ratio and meteorological environment factors and analyzed the difference of β among ecosystems, the spatial variation characteristics of β and its influencing factors. Important findings (1) The average of β in all ecosystems was 0.95 ± 0.64, the coefficient of variation of β was 67%, the skewness was 1.58, and the kurtosis was 3.07 and the variation of β follows a lognormal distribution, the shrub ecosystem has the highest mean value (1.26) and the wetland ecosystem has the lowest (0.49); (2) β is significantly different among ecosystems: β of shrub ecosystems is significantly higher than grassland ecosystems than forest and wetland ecosystems, and β of croplands is between grassland ecosystems and forest, wetland ecosystems. (3) β increases with increasing latitude and does not change with longitude and altitude. For every 1° increase in latitude, β increases by 0.038; (4) β decreases with increasing annual precipitation (MAP), annual average temperature (MAT), net radiation (Rn), one-year precipitation (PPT), one-year mean temperature (Ta), and leaf area index (LAI); (5) There are significant differences in the response of β to biotic and abiotic factors in different ecosystems: β of grassland, forest and shrub ecosystems are sensitive to changes in biotic and abiotic factors, while β of croplands and wetland ecosystems have no correlations with biotic and abiotic factors; (6) MAP and Rn are the direct factors influencing β, MAT affects β indirectly by affecting MAP, Rn and LAI, LAI affects β indirectly by affecting Rn. Our results indicate that there is an interaction between vegetation types and climatic factors. The most important factor affecting energy distribution is precipitation, and the regulation of leaf area on energy distribution is not significant.

Spatio-temporal characteristics of vegetation water use efficiency and relationship with climatic factors in alpine and subalpine area of Southwestern China

Peng-Sen SUN Ming-fang Zhang Shi-Rong LIU — 2020-05-30 00:00:00.0

Aims Water Use Efficiency(WUE) is an important indicator for understanding the coupling and trade-off relationships between ecosystem water and carbon cycles. In order to reveal the large-scale response and adaptation characteristic for different vegetation types under a context of climate change, time trends, altitudinal distribution, and spatial variation of WUE for nine vegetation types were analyzed during the study period of 2000–2014 in alpine and subalpine area of southwestern China. Methods Using 2000-2014 Moderate Resolution Imaging Spectroradiometer(MODIS) GPP and ET data, as well as Aunsplin interpolated meteorology surface data to estimate the vegetation WUE. Trend analysis, correla-tion analysis and other statistical methods were conducted to clarify the relationships between vegetation WUE and climatic factors and altitude. Important findings The result showed that: (1) As a whole, the multiyear-averaged vegetation WUE in study region was 0.95 g·m-2·mm-1 and exhibited a significant upward trend with an increasing rate of 0.011 g·m-2·mm-1· a-1(P<0.05) from 2000 to 2014. The spatial pattern of average WUE decreased gradually from the southeast to northwest and 85.84% of study area of WUE showed an increasing trend during the study period. (2) The mean WUE were evergreen needleleaf forest > savannas > evergreen broadleaf forest > woody savannas > cropland > deciduous broadleaf forest > mixed forest > closed shrublands > grassland, all vegetation types showed upward trends. (3) Correlation analysis showed that 89.56% region of WUE was positively correlated with temperature and 92.54% region of WUE was negatively correlated with precipitation, Among the vegetation types, the corre-lation between WUE of grassland and temperature was the highest, and the correlation between WUE of woody savannas and precipitation was the highest. (4) It is speculated that evergreen needleleaf forest, as the regional dominant indigenous forest type of southwestern China, has broad altitudinal adaptation and high temperature resilience of WUE.

Effects of fungal endophyte species and maternal genotype on the leaf shape and leaf area of endophyte-grass symbionts

Tian-Zi QIN An-Zhi REN Xiao-Wen FAN Yu-Bao GAO — 2020-05-30 00:00:00.0

Aims Epichlo? infection can play an important role in the growth and development of host plants. However, few studies have been reported on the effects of endophytes infection on the leaf shape and area of host plants. Methods Our study used Achnatherum sibiricum as experimental material, and explored the effects of endophyte species and plant maternal genotype on the leaf shape and area of different A. sibiricum-endophyte symbionts through the combination of the length and width method with the revised correction coefficient and the scanning calculation method. Important finding Endophyte infection status, endophyte species and plant maternal genotype had no significant influence on the leaf correction coefficient, leaf length, leaf width and leaf length-width ratio reflecting leaf shape. By calculation and verification, we determined that the leaf correction coefficient of A. sibiricum was 0.5949. There were no significant difference of the leaf area, which measured by length and width method with the revised cor-rection coefficient and the scanning calculation method. In addition, the leaf area measured by two methods was not significantly affected by endophyte infection, endophyte species and plant maternal genotype.

Characteristics of evapotranspiration of planted shrub community in the desert steppe zone based on sap flow and lysimeter methods

Long-;Long longMA Ling-Tong DU dan yang le wang Chenglong Qiao Hongyue Wu — 2020-04-30 00:00:00.0

Aims A plenty of Caragana liouana were planted in northwest China for ecological restoration which induced the planted shrub landscape emerging the desert steppe zone and changed the structure and function of the original ecosystem. The activity would affect the water vapor interactions between land surface and atmosphere eventually. Therefore, studying the evapotranspiration characteristics of the planted shrub community in the desert steppe zone is significant for us to understand its ecohydrological mechanism and guide local ecological restoration. Methods The transpiration of shrub and the evapotranspiration under shrub canopy in the desert steppe zone in Yanchi County, Ningxia Province, were measured by a coupled method of sap flow sensors and lysimeter from May to August 2018. The effects of environmental factors on the evapotranspiration of the planted shrub community were analyzed by path analysis methods. Important findings (1) The evapotranspiration obtained by the coupled method of sap flow sensors and lysimeter was consistent with the evapotranspiration calculated by the water balance method and the eddy covariance method. Thus, the coupled method of sap flow and lysimeter can be used to measure the evapotranspiration and its components of the planted shrub community in the desert steppe zone. (2) The diurnal variations of transpiration rate of shrubs and the evapotranspiration rate under shrub canopy had similar characteristics, and both presented an obvious single peak curve at noon. The evapotranspiration of planted shrub community mainly occurred in day time. However, the occurrence of the maximum transpiration rate of shrub was 1 h later than that of the maximum evapotranspiration rate under shrub canopy. (3) The cumulative transpiration of shrubs was 83.6 mm, the daily average transpiration was 0.7 mm?d?1, and the series curve of daily transpiration had a parabolic shape from May to August. The cumulative evapotranspiration under shrub canopy was 182.5 mm, and the daily average evapotranspiration was 1.5 mm?d?1 during the same period. The evapotranspiration under shrub canopy were higher than the transpiration values of shrubs, respectively. It can be concluded that the water consumption in the planted shrub community is still mainly caused by evapotranspiration under shrub canopy. (4) The total evapotranspiration of the planted shrub community from May to August was 266.1 mm, and the total precipitation in the same period was 222.6 mm. Therefore, the water cycle between land and atmosphere in the planted shrub community was in deficit. (5) Net radiation is the most important and direct driving factor that affected evapotranspiration of the planted shrub community, and it coupled other environmental factors to drive the process of evapotranspiration. Therefore, the water deficits between land and atmosphere that caused by planted shrub encroaching desert steppe zone should be paid attention in ecological restoration and reconstruction.

Study on the patterns of genetic variation of Lycium ruthenicum in Qaidam Basin

WANG chuncheng Song-Mei MA ZHANG dan Shao-Ming WANG — 2020-04-30 00:00:00.0

Aims Based on the cpDNA sequences, we aimed to analyze the distribution of genetic variation, genetic differentiation and haplotype evolution of the wild L. ruthenicum in Qaidam and provide scientific basis for populations' conservation. Methods Based on the filtered highly polymorphic cpDNA fragments (psbA-trnH, psbK-psbI and trnV), we sequenced 60 samples from five wild L. ruthenicum populations in Qaidam. AMOVA analysis was employed to estimate genetic differentiation among populations, maximum likelihood method and Bayesian method were used to reconstruct the phylogenetic tree based on cpDNA haplotypes. Important findings The combined lengths of psbA-trnH, psbK-psbI and trnV was 1542 bp, 14 polymorphic sites were detected, and a total of 7 haplotypes were identified. The total genetic diversity (hT) and within-population genetic diversity (hS) were 0.916 and 0.512, respectively. Results from AMOVA suggested that more than 80% of the observed variation was due to differences among groups. The haplotype maximum likelihood tree and Bayesian phylogenetic tree of chloroplast haplotypes show that the studied L. ruthenicum in the distribution area are clustered into two clades: the populations in the Golmud and Delingha for one clade, the populations in Nuomuhong for the other. The revealed topological structure of haplotype network and PCoA analysis is consistent with the phylogenetic tree. Mantel test result indicating that there is a significant weak correlation of genetic distance with geographic distance among populations of L. ruthenicum in Qaidam Basin (r = 0.5911，P = 0.0009). The population of L. ruthenicum in Qaidam Basin has high genetic diversity and significant genetic differentiation among populations. From the conservation perspective of genetic diversity, the populations of NMH1 and GEM1 with high genetic diversity can be divided into conservation management units.

Defense strategies of dominant plants under different grazing intensity in typical temperate steppe of Inner Mongolia, China

2020-04-03 00:00:00.0

Aims Grazing is one of the main grassland using modes, which has caused certain biotic stress on pasture. In order to survive, pasture initiates defense mechanisms by regulating the primary and secondary metabolic processes. This article aims 1) to figure out the distribution of defensive substances in different organs produced by the dominant plants Stipa grandis and Leymus chinensis; 2) to explore the similarities and differences of the defense mechanisms and carbon-nitrogen trade-off strategies in S. grandis and L. chinensis. Methods We conducted a different grazing intensity experiment in typical temperate steppe of Nei Mongol. The lignin and secondary metabolites, such as tannins, flavonoids, phenols and alkaloids, as well as the ratio of carbon and nitrogen in different organs of the dominant plants S. grandis and L. chinensis were investigated. Important findings Our results showed that S. grandis and L. chinensis produced a large number of secondary metabolites such as tannins, flavonoids, phenols and alkaloids in the face of grazing stress. The leaves were the main synthesis and storage organs. In addition, the chemical defense mechanism of L. chinensis was well induced and expressed under moderate grazing. There was no significant increase in the lignin content in the aboveground parts of S. grandis and L. chinensis. Therefore, both of them were more inclined to chemical defense than mechanical defense in the mechanism of avoiding grazing. Because of the higher nitrogen use efficiency of L. chinensis, it could be protected by both carbon and nitrogen metabolic pathways. However, Stipa grandis did not efficiently distribute nitrogen into chemical defense in the early stages of growth. More resources still used for primary metabolism in the early stage of S. grandis and L. chinensis growth, under light grazing stress, which increased their grazing resistance. Therefore, light grazing is conducive to improving the carbon and nitrogen use efficiency of pasture, and improving ecosystem productivity and stability.

Spatial variation and effect factors of temperature sensitivity of soil respiration in China’s forest ecosystems

Jia-Jia ZHENG Xin JIA Song-Yu HUANG Yu MU Peng LIU — 2020-03-26 00:00:00.0

Aims：Our objective was to determine the spatial variation of temperature sensitivity of soil respiration (Q10) and it’s controlling factors in forest ecosystems across China. Methods：Based on published papers, the field measurement data of soil respiration were collected to build the dataset of annual Q10 for in forest ecosystems across China. Further, the spatial variation and the drivers of Q10 in different forest types were analyzed. Important findings：The results showed that 1) Q10 ranges from 1.09 to 6.24, with a mean value(± standard error) of 2.37( ± 0.04) and there is no significant difference among different forest types; 2) When all forest types were considered, Q10 increased with increasing latitude(Lat ), altitude(Alt), soil organic carbon (SOC) and soil total nitrogen (TN), but decreased with increasing longitude(Lon), mean annual temperature (MAT) and mean annual precipitation (MAP). Climate (MAT, MAP) and soil (SOC, TN) factors together explained 32.8% variations in Q10. MAT and SOC were considered as the primary factors driving the spatial variation in Q10. 3) The Q10 of different forest types responded differently to climate and soil factors. Q10 decreased with the increase of MAP, while Q10 showed no significant correlation with MAP in other forest types. Q10 increased with the increase of TN in evergreen broadleaved forest (EBF), deciduous broadleaved forest (DBF), evergreen needleleaf forest (ENF), and the sensitivity of Q10 to TN was the highest in EBF and the lowest in ENF. Although Q10 showed concentrated distribution trend, more attention should be paid to the large variation range in future C estimation works. The primary driving factors and the response to environmental factors of Q10 varied among forest types. Under the scenario of future climate change, Q10 may vary divergently among different forest types. Therefore, the divergent responses of key parameters of carbon cycle in different forest types to climate change should also be considered in future carbon–climate models.