Plants have constructed diverse defense strategies in response to herbivory over time, with chemical defenses based on plant secondary metabolites playing a key regulatory role in plants-herbivores interspecific interactions. The biosynthesis of plant secondary metabolites is a trade-off strategy for plants to cope with herbivores at the cost of reduced resource allocation to growth and reproduction. Recently, numerous studies have been conducted on how plant secondary metabolites affect behavior of herbivores, individual growth and fitness of plants. However, a comprehensive and in-depth elaboration of the chemical defense strategies of plants is still lacking. This study provides a systematic review of the factors influencing the synthesis and release of plant secondary metabolites, the chemical defense strategies and their formation mechanisms in response to herbivory. Individual plant tissues and organs, population and species composition in the community, species and feeding intensity of herbivores, soil resource availability, growing seasons, environmental stresses all can affect the synthesis and release of plant secondary metabolites. Meanwhile, plants respond to herbivory by enhancing the plasticity of chemical defense, regulating the partitioning pattern of photosynthetic products and the trade-offs relationship between growth, reproduction and defense. The growth-differentiation balance hypothesis, plant apparency hypothesis, optimal defense theory, carbon/nutrient balance hypothesis, growth rate hypothesis, plant defense syndromes hypothesis and error management theory are the main hypotheses used to explain the mechanism of plant chemical defense strategies. As human activities (e.g., grazing) increase and climate change intensifies, researches on plant defense strategies in response to large herbivore feeding, environmental stress and global change should be strengthened in the future from a multidisciplinary perspective, which will be helpful for deeper understanding of the defense processes and mechanisms of plants in response to herbivores.

Biogenic volatile organic compounds (BVOCs) are secondary metabolites of plants that play various ecological roles, such as defense and signaling. They have become a popular topic in environmental and ecological studies. Nitrogen deposition is a dual factor of nutrient and environmental stress for plants that alters the emission of plant defense-related BVOCs (dBVOCs). It affects inter-species communication, their survival and development, and structure and function of the entire ecosystem. However, relevant research is limited. In this study, we focused on three types of dBVOCs, namely, terpenes, green leaf volatiles, and methyl salicylate, and elucidated their main components, synthesis pathways, ecological functions, and responses to various biotic and abiotic stressors. We further examined the impact of nitrogen deposition on these dBVOCs, exploring their response trends and related mechanisms under nitrogen–phosphorus limitation. Future research is necessary to deepen and expand the understanding of dBVOCs by uncovering their underlying mechanisms. Additionally, efforts should be made to overcome the challenges in research methods and detection devices for dBVOCs and strengthen interdisciplinary collaboration. Such advancements can provide theoretical support for tree planting management, green pest prevention and control, and promotion of sustainable development in the context of global changes.

Aims： Under the background of global climate change, frequent extreme precipitation events will affect the soil nitrogen transformation process in the semi-arid steppe. However, how the key processes of soil nitrogen transformation respond to precipitation change and the sensitivity of total nitrogen mineralization rate to different precipitation levels remains unclear. Methods： In this study, the gross nitrogen mineralization rate (GNM), and gross nitrification rate (GN) of soil were measured by the 15N pool dilution method based on meadow steppe, typical steppe, and desert steppe of the Global Change Network test platform of northern China Steppe. And related biological (microbial biomass carbon, microbial biomass nitrogen, background biomass (BGB)), and abiotic (soil temperature (ST), soil water content (SWC)) soil substrate (soil ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3--N, soluble organic carbon, soluble organic nitrogen) indexes. Important findings：The results showed that there were significant differences in GNM among different steppe types. The highest GNM was in meadow steppe (3.284 ± 0.613mg·kg-1·d-1), followed with typical steppe (1.370 ± 0.167 mg·kg-1·d-1) and desert steppe (0.724 ± 0.216 mg·kg-1·d-1). However, A 50% decrease in rainfall had no significant effect on GNM and GN of the three grasslands. The sensitivity of GNM and GN to precipitation reduction in typical steppe and desert steppe soil were significantly higher than that of precipitation increase, while the sensitivity of GNM and GN in meadow steppe soil was not significantly different between precipitation increase and decrease. Structural equation model (SEM) analysis revealed that soil moisture was the main factor affecting soil GNM. These results indicate that short-term extreme precipitation has no significant effect on GNM and GN of three important grasslands in northern China, but changes their sensitivity to precipitation change. How the increase of extreme precipitation events will affect the soil nitrogen conversion process in terrestrial ecosystems in the future needs to be systematically studied on long-term scales and large spatial patterns.

Aims In the saline–alkaline grassland of the agro-pastoral ecotone with limited nutrients, the increase of nitrogen input induced by agricultural fertilization and the change of land use patterns usually cause changes in soil available nutrients, which further affect the net primary productivity of plants. However, due to the impact of inter-annual precipitation, there is still great uncertainty about whether the response of net primary productivity of plants to nitrogen addition and mowing will vary with changes in rainfall. Methods This study takes saline-alkali grassland in the agro-pastoral ecotone of northern China as the research object, relies on the experimental platform for nitrogen forms and mowing at the National Research Station of Grassland Ecosystems on the Loess Plateau in Youyu, Shanxi Province, and experiments with six treatments including control and simulated nitrogen deposition experiments with two common nitrogen compounds (ammonium nitrate and urea), with and without mowing. The response of plant net primary productivity to nitrogen addition and mowing was studied. Important findings The results showed that: (1) Regardless of mowing or un-mowing treatments, short-term addition of ammonium nitrate and urea significantly increased the content of inorganic nitrogen in the soil, thereby increasing the aboveground (ANPP), belowground (BNPP), and total net primary productivity (NPP); (2) ANPP, BNPP, NPP, inorganic nitrogen content, and soil water content showed significant interannual differences, with higher values observed in the wet year (2018) than in the dry year (2017); (3) The interaction between short-term nitrogen addition and year had a significant impact on NPP. In the wet year, NPP was significantly higher under nitrogen addition than in the dry year. In the wet year, the positive effect of nitrogen addition on NPP was significantly higher than that in the dry year, which was mainly related to the synergistic effect of soil nitrogen and water; (4) Mowing decreased NPP and had a significant interactive effect with the year on the BNPP/ANPP. In the dry year, mowing generally decreased BNPP/ANPP. However, in the wet year, this negative effect gradually weakened and even turned into a positive effect. These results emphasize the crucial role of natural precipitation in regulating the response of net primary productivity of saline-alkali grassland in the agro-pastoral ecotone to anthropogenic disturbances, and further indicate that the saline-alkali grassland ecosystem in the agro-pastoral ecotone is jointly limited by nitrogen and water.

Aims The objective of this study was to explore the effects of long-term nitrogen (N) addition on leaf litter production and nutrient return by the dominant tree species in broadleaf evergreen forests of subtropical regions. Methods A long-term N addition manipulation experiment with three levels (0 kg·hm-2·a-1, CK; 20 kg·hm-2·a-1, LN; and 40 kg·hm-2·a-1, HN) was conducted to examine the effects of N addition on leaf litter production, contents of leaf litter carbon (C), N, and phosphorus (P), as well as their return within Michelia wilsonii forests located on the western margin of the Sichuan basin. Important findings (1) Significant inter-annual variations were observed in the production of M. wilsonii leaf litter, as well as in the mean contents of C, N, and P and their annual return, but N addition did not affect these inter-annual dynamics. (2) The HN treatment significantly increased the annual leaf litter production of M. wilsonii by 24.9%. Additionally, the effect of N addition on the average annual litter production decreased as the duration of N addition increased. (3) The HN treatment resulted in a significant increase in the mean annual content of C in by 3.4%. The effects of HN treatment on leaf litter N and P content exhibited a turning point during the 2019-2020 interval, coinciding with notable alterations in the annual average N content in leaf litter. Specifically, the annual average N content was suppressed in both 2018 and 2019, but then experienced a significant increase in 2020. In contrast, a general downward trend was observed in the P content from 2016 to 2019. (4) N addition significantly increased the annual return of C, N, and P in leaf litter, with the promotional effect intensifying as the level of N addition increased. However, the effect of N addition on the annual P return showed a significant linear decline trend over the study period. These findings highlight that high N additions significantly promoted the productivity of M. wilsonii forests and augment carbon and nutrient inputs within the ecosystem Distinct effects of short-term versus long-term N inputs on the N cycling processes of M. wilsonii forest ecosystems were observed. Additionally, the future exogenous N addition may potentially inhibit the leaf litter yield and P return of M. wilsonii.

Aims Plants and soil microorganisms play crucial roles in regulating the function and stability of terrestrial ecosystems. Exploring the pattern variations of the community composition and diversity of plant and soil microorganisms and their driving mechanisms along elevation gradients is better understanding their response to terrestrial ecosystems and the maintenance mechanisms of biodiversity under global change. Methods In this paper, we designed a vertical gradient experiment with three different grassland types in the northern slope of Kunlun Mountain. Through community investigation in field with climate data, and high-throughput sequencing was used to assess soil microbial for baterial 16S RNA and fungal internal transcribed spacer(ITS) regions on Illumina NovaSeq. The variation patterns of community structure, composition and species diversity of plant and soil microorganisms along altitude gradient (2 200–3 800 m) and their potential relationships were studied. Important findings (1) The species diversity and productivity of aboveground plant community, soil microorganism’s diversity (including bacteria and fungi) and soil nutrients increased monotonously along the altitude gradient, and the peak value was found in the alpine steppe. Soil fungi were more sensitive to environmental gradient than bacteria. Aboveground plant community and soil fungal community had a significant variation along altitude gradient, but the structure and composition of soil bacterial community did not change significantly. Species diversity and aboveground biomass of plant community were significantly related to the diversity of soil microbial community, but the relationship with bacterial diversity was stronger than that of fungi. The species diversity of soil microorganisms and plant community was positively correlated with mean annual precipitation (MAP) and soil nutrients (carbon, phosphorus and potassium) content, but negatively correlated with mean annual air temperature (MAT). The pattern analysis showed that altitude (geographical distance) and climate factors had greater contribution on soil microorganisms and plant biodiversity than soil factors. The variation of climate factors (MAT and MAP) caused by altitude gradient were the dominant driving factors for community dynamics of plant and soil microorganisms, but their roles were different. Soil nutrients also play an important role in biodiversity of soil microorganisms and plant community. In summary, the regional distribution pattern of aboveground plant and soil microbial communities in mountain steppe is co-regulated by climate and soil factors caused by altitude gradient in the arid region. This study revealed that climatic factors in arid areas were the dominant factors that drive the variations of distribution pattern and structural composition of plant and soil microbial communities in mountain steppe ecosystems, and soil microbial diversity (especially bacteria) played a vital role in improving the productivity of grassland communities. This research provides scientific guidance for grassland ecosystem management and biodiversity protection in arid areas.

Aims In order to understand the interspecies competition strategy of the new fruit - bean agroforestry system and find a planting pattern that balances ecological and economic benefits, the Malus pumila 'Saiwaihong' - Glycine max agroforestry system (MS) was set up. Methods Through the study on root length density (RLD), specific root length (SRL), root vertical center, competitiveness index and interspecific relative competitiveness of the Malus pumila 'Saiwaihong' - Glycine max agroforestry system, the interspecific competition strategy was revealed. Important findings The results showed that the RLD of intercropping fruit trees and soybean was lower than that of monoculture, and the trend of SRL was opposite. Soybean roots were mainly distributed at 0-20 cm soil depth and 150-200 cm away from the tree, and decreased with the increase of soil depth and the decrease of distance from the tree. The root system of intercropping malus mainly distributed in the soil depth of 20-40 cm. With the growth period, the vertical center of fine roots moved downward. In the Malus pumila 'Saiwaihong' - Glycine max agroforestry system, each plant adopted different interspecific competition strategies. Fine roots of soybean became a strong competitor in the surface soil of the Malus pumila 'Saiwaihong' - Glycine max agroforestry system by increasing SRL and reducing root weight. Intercropping Malus could reduce niche overlap and resource competition with intercropping soybean by moving down the root distribution center, lengthening root length and increasing root weight. The overall interspecific relative competitiveness of malus was stronger than that of soybean, but the competitiveness index of soybean was still stronger than that of malus in the topsoil. The yield of intercropping soybean was 34.12% lower than that of monoculture. There was no significant difference in the yield of malus. The land equivalent ratio (LER) and income equivalent ratio (IER) of the agroforestry system were greater than 1. The results showed that the underground competition of Malus pumila 'Saiwaihong' - Glycine max agroforestry system was weak, and it had good intercropping advantages which were suitable for planting in Xinjiang province. The results of this study can provide a reference for the selection of planting patterns of agroforestry systems in arid and semi-arid areas.

Aims To understand the current state of the population of Fraxinus sogdiana, a second-grade endangered species in China, and predict its development trend, a large sample survey was conducted in the Xinjiang Ili Fraxinus sogdiana National Nature Reserve. Methods By replacing the age structure with the diameter at breast height structure, a population static life table was compiled and related population structure was analyzed. The survival curve, mortality curve and survival analysis function curve were drawn, and population dynamic index was calculated, and the population fluctuation cycle was explored via using spectral analysis. Important findings 1) The populations of F. sogdiana on the east and west of the Kashi River and total population exhibited growing age structure, with the survival curves towards Deevey-II type. 2) The mortality peaks for the population on the east of the Kashi River and total population were in the age classes of Ⅳ, Ⅶ, and Ⅹ, while those on the west of Kashi River population class had a mortality peak in age class V. 3) The dynamic change index ignoring the external interference (Vpi) and dynamic change index under external interference of the populations on the east and west of the Kashi River and total population were greater than 0, indicating that they were growing-type populations. But the of population on the east of the Kashi River was close to 0, suggesting that it was more resistant to external random environmental interference. 4) Survival analysis revealed that the survival rate and cumulative mortality rate of populations in different habitats reached equilibrium in age classes II–III. The hazard rate curve of the population on the east of the Kashi River exhibited relatively smaller fluctuations, indicating that this area is more suitable for the growth of F. sogdiana. 5) Spectral analysis showed that the fluctuations of F. sogdiana populations are primarily controlled by their own biological characteristics. The population on the east of the Kashi River and total population exhibited small cycle fluctuation characteristics with multiple harmonics superimposed during the large cycle. It is recommended protecting and improving habitat of F. sogdiana, accurately nurturing individuals in age classes I and II, and promoting the natural regeneration and development of the population.

Alfalfa (Medicago sativa L.) is an important forage in the intercropping system. However, the extreme weak light environment in the intercropping system often leads to a significant decrease in alfalfa yield, and breeding shade-tolerant cultivars is the main way to solve this bottleneck problem. In this experiment, 20 alfalfa germplasm resources were used as test materials, and the shading rates were 0% (full light), 52.9% and 71.8%. Three shading treatments were used to determine the changes in six morphological indexes (stem diameter, height, primary lateral root, root nodule, root crown tiller, angle of stem to leaf), seven growth indexes (leaf weight, plant biomass, leaf area, specific leaf area, leaf mass ratio, stem mass ratio, root mass ratio), and five physiological indexes (chlorophyll a content, chlorophyll b content, total chlorophyll content, carotenoid, chlorophyll a/b ratio) during the tillering stage of alfalfa under different light intensities. Based on the shading tolerance coefficients of 0% and 52.9%, principal component analysis, membership function analysis, cluster analysis, and stepwise regression analysis were used to comprehensively evaluate the shade tolerance of alfalfa germplasm resources and screen their identification indicators. The results showed that the stem diameter, the number of root nodule, and the number of root neck tillering of alfalfa decreased with the decrease of light intensity. The total chlorophyll content showed an increasing trend. The number of primary lateral root, leaf dry weight, biomass per plant, and leaf area showed a trend of first increasing and then decreasing, while the trends of other indexes were inconsistent, and there were significant differences among different cultivars. Combining principal component analysis, membership function analysis and cluster analysis, the 20 test materials could be divided into three types according to their shade tolerance: shade tolerant (4 test materials), semi-shade tolerant (8 test materials), and sensitive (8 test materials). By stepwise regression analysis, the optimal regression equation was established: D=-0.108+0.071X10+0.049X6+0.208X14+0.027X4+0.096X7+0.052X3+0.048X5, the precision of estimation was above 93.72%, Seven indexes, including leaf area, leaf dry weight, angle between stem and leaf, number of root nodules, primary lateral roots, number of root neck tillering, and chlorophyll a content were selected as shade tolerance identification indexes of alfalfa. The research results can provide good materials and scientific basis for the breeding of alfalfa cultivars with shade tolerance, and contribute to the construction and optimization of alfalfa intercropping systems.

The aim of this study was to better understand the regulatory mechanism of growth and development of Reaumuria songorica seedlings, and to provide some references for the cultivation and restoration of desert plants.This study uses one-year-old seedlings of R. songorica as materials to investigate the effects of photoperiods and light quality ratios on their growth.LED lights were used as the light source, and three photoperiods and six light quality ratios were set up for cross-cultivation. The plant height, branch number, biomass and photosynthetic pigment content of the R. songorica seedlings were measured to evaluate their growth, and the effects of photoperiod and light quality ratio on their growth were investigated.The proper photoperiod and light quality ratio played an important role in the growth and development of R. songorica seedlings. Increasing the light time can promote the growth of R. songorica. When the ratio of red to blue was 3:1, the growth rate of plant height increased by 20.20% and 88.47% for 14 and 16 hours compared with 12 hours, respectively. When the ratio of red to blue light was 1:3 and the daily light duration was 14 and 16 hours, the number of primary branches increased by 6.67% and 66.67%, and the underground biomass increased by 259.85% and 551.82%, respectively. High proportion of red light and high proportion of blue light treatment can promote the growth of R. songorica seedlings, but the growth rate of plant height and the change trend of primary branch number is opposite. Under the light quality ratio of R:B=4:1, the growth rate of plant height increased with photoperiod, while the number of primary branches decreased. However, under the light quality ratio of R:B=1:4, the growth rate of plant height and the number of primary branches were opposite. Through the comprehensive application of principal component analysis and membership function analysis, the results show that the growth condition of R. songorica seedlings is better under treatments T2 (12-hour light, red-blue light ratio of 4:1) and T5 (12-hour light, red-blue light ratio of 1:4).

The Zada Xiangquan River valley in the western part of Ngari prefecture is one of the main distribution areas of the mountainous desert on the Qinghai-Tibet Plateau, but there is a lack of data on desert vegetation in this area. In order to find out the background of desert vegetation in this area, this study was based on the field survey of 42 desert sample plots in Zada County, Nagri, Tibet from 2018~2023, and the classification and community characteristics of desert vegetation in the basin were analyzed. The results showed that there were 8 desert alliances in Zada County, Tibet, including 2 temperate shrub deserts: Caragana versicolor desert and Ephedra intermedia desert, and 6 temperate semi-shrub and herbaceous deserts, Ajania fruticulosa desert, Ephedra gerardiana desert, Krascheninnikovia ceratoides desert, Krascheninnikovia eversmanniana desert, Lactuca orientalis desert and Seriphidium thomsonianum desert, Notably, 5 desert alliances (C. versicolor, E. gerardiana, K. eversmanniana, L. orientalis, and S. thomsonianum deserts) are newly recorded desert types.. A total of 82 species of vascular plants belonging to 51 genera belonging to 20 families were recorded, Among them, the life forms are mainly hemicryptophytes and perennial forbs . The ecological type for water were mostly hyperxerophytic and typical xerophytes, including most of the building and associated species of desert vegetation, such as Ajania fruticulosa, Ephedra intermedia, Krascheninnikovia ceratoides, Lactuca orientalis, Krascheninnikovia eversmanniana, etc. The Central Asian-Asian component is the most important component of the geographical floristic type, followed by the Tibetan Plateau and the Eastern Paleoarctic. The results of this study provide basic data and information for understanding the status and distribution characteristics of desert vegetation resources in this region, clarifying the types and characteristics of desert vegetation in the Qinghai-Tibet Plateau, and regional biodiversity conservation.