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 of 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.

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. 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 the inter-species level on the Qinghai-Xizang Plateau.
Methods In the alpine meadows of Qinghai-Xizang 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 the 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 the inter-species level at low and high habitats.
Important findings 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 increase the female fitness of plants in low-altitude communities, However, the female fitness of plants is only associated with flower longevity in high-altitude communities. Overall, our results suggest that flower longevity is more important for the female fitness in high-altitude plants than low-altitude plants.

Aims Biological soil crust is an important type of surface cover in alpine sandy lands. Understanding of the effect of warming on respiration from the biological soil crust-soil system in alpine regions can provide theoretical reference to the assessment of the response and feedback of biological soil crusts to climate changes.
Methods The moss and algae crusts in the artificial vegetation restoration areas were taken as the research objects. The open top chamber (OTC) was used as a passive warming device to simulate warming. The daily and growing season dynamics of respiration rates in two types of biological soil crust-soil systems were measured. The effects of warming on CO₂ emission and its temperature sensitivity were discussed.
Important findings Both the daily and the growing season dynamics of respiration rate of the moss and algae crust-soil system showed “single-peak” curves and were not affected by warming. The daily peaks appeared around 13:00, and the growing season peaks appeared around August. Warming changed the daily peak value of respiration rate of the biological soil crust-soil system. In the relatively dry year (2017), moderate warming increased cumulative CO₂ emission from the two types of biological soil crust-soil system during growing season, but the increase declined under excessive warming. In the relatively wet year (2018), as warming got greater, CO₂ emission from the two types of biological soil crust-soil system increased more. The relationship between respiration rate and temperature of two types of biological soil crust-soil system followed the exponential function. In the relatively dry year, more increase of temperature induced smaller temperature sensitivity of CO₂ emission, and the temperature sensitivity varied from 1.47 to 1.61 and 1.60 to 1.95 in the moss and algae crust soil system respectively. In the relatively wet year, with the increase of temperature, temperature sensitivity of system respiration increased, and the temperature sensitivity varied from 1.44 to 1.68 and 1.44 to 1.76 in the moss and algae crust soil system respectively. This study shows that global warming has greatly increased the respiration of biological soil crust-soil system in alpine ecosystems. Therefore, we should fully consider the impact of climate warming on the wide spread biological soil crusts in this area for better evaluation of carbon cycling processes in alpine ecosystems.

Aims 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. Legumes, an important component of grassland ecosystems, would be significantly affected nutrient addition. This study aims to clarify the effects of nutrient addition on the functional traits of legumes.
Methods We carried out a nutrient addition experiment in Onqin Daga Sandy Land, in which different amount of chicken manure (CMA, L0-L6 were 0, 500, 1 000, 1 500, 2 000, 2 500 and 3 000 kg·hm_-2·a^-1) was used as the nutrients. Then we explored the effects of nutrient addition on Melilotus officinalis, a typical legume plant.
Important findings The results showed that the leaf nitrogen (N), phosphorus (P), potassium (K) content, maximum photosynthetic rate (P_nmax), 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 3 000 kg·hm_-2·a^-1 (L6), the leaf N, P, and K content of M. officinalis increased by 15%, 67% and 25% respectively compared with L0. CMA also influenced H, SLA, P_nmax and WUE of M. officinalis, and the responses of these functional traits to CMA was hump shaped. When CMA amount was lower than 1 500 kg·hm_-2·a^-1 (L3), H, SLA, P_nmax and WUE of M. officinalis in August increased significantly by 51%, 18%, 12% and 38% respectively; when CMA amount was higher than 1 500 kg·hm_-2·a^-1 they all decreased significantly. There was no significant difference in the values of H, SLA, P_nmax and WUE 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 improve the maintenance of their population.

Aims Variations of many branch traits are affected by plant size, branch age and environment factors, but the relative 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 (diameter at breast height (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 0.3-100.0 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 (R_XA), the phloem area-to-total cross-sectional area ratio (R_PHA) and the pith area-to-total cross-sectional area ratio (R_PA) were more sensitive to DBH, while the total resin canal area-to-total cross-sectional area ratio (R_RC) and wood nitrogen content (WN) were more affected by the tree height; (2) branch age was the most important factor in driving intra-specific variations of branch traits of P. koraiensis, followed by plant size, while the impact of environment factors was minimal; (3) WD and R_PHA were significantly positively correlated with DBH, while R_PA was significantly negatively correlated with DBH; and R_RC 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 R_RC decreasing with branch age was enhanced, but the rate of R_PA decreasing with branch age was weakened. The results of our study are helpful to understand the driving factors of intraspecific variation of branch traits at the local scale and the adaptation mechanism of branches to cope with environmental changes.

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 prompt the rapid recovery of the damaged G. uralensis natural population. Appropriate external disturbance is always beneficial to the growth and reproduction of clonal plants such as G. uralensis due to plant clonality. But the roles and mechanisms of disturbances and plant clonality in the recovery of damaged G. uralensis natural populations 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 individual ramets of G. uralensis in the natural population, suggesting the same compensation growth in G. uralensis. In contrast, G. uralensis showed different responses to severe disturbances, depending on the disturbance type. Significantly lower ramet density, height and shoot biomass of individual ramets were observed in G. uralensis under severe clipping treatment, indicating undercompensated growth; while significantly higher ramet height, shoot biomass of individual ramets and also total shoot biomass of plant population were observed under severe digging out treatment, suggesting 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, suggesting that disturbance at certain levels may improve the medicinal material quality of G. uralensis.

Aims The objectives of this study were to estimate the adaptation strategies of Broussonetia papyrifera to the poor soil nutrients in karst rocky desertification area in Southwest China, and to explore the response of stoichiometric characteristics of fine roots and rhizosphere soil to the degree of rocky desertification.
Methods The contents of carbon (C), nitrogen (N), phosphorus (P), calcium (Ca), magnesium (Mg) and C:N:P ratios of fine roots and rhizosphere soil of B. papyrifera were studied.
Important findings Results indicated that, except Ca content, the nutrient content of the fine roots and rhizosphere soil of B. papyrifera in karst rocky desertification environment remained at the low level. N:P ratio of fine roots was 12.59, which indicated that the growth of B. papyrifera was co-limited by N and P. With the increase of the degree of rocky desertification, the content of C and N as well as C:N and C:P ratios of fine roots decreased first and then increased; while the content of K and P increased first and then decreased; and neither the content of Ca, Mg nor N:P ratio changed significantly. The content of N, P, K, Ca in rhizosphere soil was different when the degree of rocky desertification was different, while none of C, Mg and C:N:P ratios in rhizosphere soil changed significantly. Additionally, the content of C, P, Ca, Mg as well as C:N and C:P ratios in the fine roots were positively correlated with their values in rhizosphere soil, while N content in fine roots was negatively correlated with its value in the rhizosphere soil. Moreover, the content of K in fine roots was relatively stable, and was hardly affected by the nutrients of rhizosphere soil.

Aims Regeneration of sub-alpine forests have an capacity to sequester carbon and nitrogen. Our objectives were to quantify variations of soil organic carbon and nitrogen content and enzyme activities at different successional stages of natural secondary forests, and to better understand the underlying mechanisms of carbon and nitrogen sequestration in these sub-alpine forests.
Methods We used the space-for-time substitution method and selected four sub-alpine forests in Miyaluo forest of Western Sichuan, China. The secondary forests were at different successional stages with natural regeneration on cutting-blanks in 1960s (60-NSF), 1970s (70-NSF) and 1980s (80-NSF), and the Abies faxoniana primary forest was used as control (CK). The soil samples were taken from 0 to 20 cm depths in each forest 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) content and soil enzyme activities were measured. The activities of five soil extracellular enzymes related to soil carbon and nitrogen cycling were determined to explain their relationships with soil physico-chemical properties.
Important findings The contents of topsoil SOC, DOC, LFOC decreased with succession stage, whereas TN and DON were all in the order of 60-NSF < 80-NSF < 70-NSF, although 80-NSF and 70-NSF exhibited no significant difference. The topsoil organic carbon and nitrogen and their active fractions contents in natural secondary forests were lower than those in the primary forest, while no significant difference in DOC and DON contents was observed between 80-NSF and CK. The activities of soil β-4-glucosidase (βG), β-4-N-acetylglucosa- minidase (NAG) and polyphenol oxidase (PHO) in CK were significantly higher than those in natural secondary forests, whereas soil cellulose hydrolysis (CBH) and phenol oxidase (PEO) activities had no significant difference between secondary forests and CK. Activities of βG and CBH in 60-NSF were significantly lower than those in 70-NSF and 80-NSF, but activities of NAG in 80-NSF were significantly higher than those in 60-NSFand 70-NSF. There was no significant difference in PEO activities among different types of forest. Both Pearson correlation analysis and redundancy analysis showed that soil enzyme activities were significantly correlated with soil TN, LFOC and DOC contents. TN content explained 65.4% of the variations in enzyme activity, which implied that change in soil nitrogen content might affect C-related hydrolytic enzyme activities (e.g. βG, CBH and NAG). Meanwhile soil microorganisms prefer to use readily decomposable carbon and nitrogen. Therefore, activities of some soil enzymes such as βG, CBH and NAG in natural secondary forests decreased due to the declines in soil TN, LFOC and DOC contents. We conclude that soil enzyme activities could be more favorable to C and N cycling in the Abies faxoniana primary forest than in the secondary forest at the early-successional stages (<60 a) in high-altitude sub-alpine forest ecosystems in Western Sichuan, China.

The Stipa bungeana alliance is one of the main steppe types in Eurasian. Endemic to China, the alliance is mainly found in the Loess Plateau and the adjacent areas, but its range of distribution has been noted to decline and become highly fragmented due to conversion to cropland or at unstable successional stages. In this study, we described and analyzed the eco-geographical distribution, community characteristics, and vegetation classification of S. bugneana alliance based on data from 108 plots surveyed during 2013-2019. Results show that S. bungeana alliance is currently distributed in northern Shaanxi, southern Ningxia, eastern and central Gansu, northern Shanxi, the loess hills in the south of Yinshan Mountains and the Erdos Plateau. This alliance occurs mainly on loess soils or kastanozems, along elevation ranging from (1) 631 to 3 174 (4 098) m. Two hundred and fourteen plant species from 37 families and 109 genera were recorded across the 108 plots, with most of them being rare species in the alliance. There are more hemicryptophytes and perennial forbs than other life forms. Xerophytes, especially meso-xerophytes and typical xerophytes, have higher representation in species richness than mesophytes. Among the 10 geographical floristic elements, the East Asia element, the East Palearctic element and the central Asia element were the three dominants. The height, cover, biomass and species richness vary greatly across the plots because those variables are highly related to the moisture and disturbance intensity of the habitats. Based on China Vegetation Classification System, S. bugneana alliance could be classified into seven association groups and 37 associations.