The primary mechanisms contributing to nitrogen (N) addition induced grassland biodiversity loss, namely light competition and soil cation toxicity, are often examined separately in various studies. However, their relative significance in governing biodiversity loss along N addition gradient remains unclear. We conducted a 4-yr field experiment with five N addition rates (0, 2, 10, 20, and 50 g N m-2 yr-1) and performed a meta-analysis using global data from 239 observations in N-fertilized grassland ecosystems. Results from our field experiment and meta-analysis indicate that both light competition and soil cation (e.g. Mn2+ and Al3+) toxicity contribute to plant diversity loss under N enrichment. The relative importance of these mechanisms varied with N enrichment intensity. Light competition played a more significant role in influencing species richness under low N addition (≤ 10 g m-2 yr-1), while cation toxicity became increasingly dominant in reducing biodiversity under high N addition (>10 g m-2 yr-1). Therefore, a transition from light competition to cation toxicity occurs with increasing N availability. These findings imply that the biodiversity loss along the N gradient is regulated by distinct mechanisms, necessitating the adoption of differential management strategies to mitigate diversity loss under varying intensities of N enrichment.

Recent droughts have strongly impacted forest ecosystems and are projected to increase in frequency, intensity, and duration in the future together with continued warming. While evidence suggests that tree diversity can regulate drought impacts in natural forests, few studies examine whether mixed tree plantations are more resistant to the impacts of severe droughts. Using natural variations in leaf carbon (C) and nitrogen (N) isotopic ratios, that is δ13C and δ15N, as proxies for drought response, we analyzed the effects of tree species richness on the functional responses of tree plantations to the pan-European 2018 summer drought in seven European tree diversity experiments. We found that leaf δ13C decreased with increasing tree species richness, indicating less drought stress. This effect was not related to drought intensity, nor desiccation tolerance of the tree species. Leaf δ15N increased with drought intensity, indicating a shift toward more open N cycling as water availability diminishes. Additionally, drought intensity was observed to alter the influence of tree species richness on leaf δ15N from weakly negative under low drought intensity to weakly positive under high drought intensity. Overall, our findings suggest that dual leaf isotope analysis helps understand the interaction between drought, nutrients, and species richness.

Amphibians serve as reliable indicators of ecosystem health and are the most threatened group of vertebrates. Studies on their spatial distribution pattern and threats are crucial to formulate conservation strategies. Gongga Mountains, with a peak at 7509 m a.s.l. and running latitudinally, are in the center of the Hengduan Mountains Range and at the eastern steep edge of the Qinghai-Xizang Plateau, providing heterogeneous habitats and varied niches for amphibians. In this study, we combined 83 days of field work with information from 3894 museum specimens that were collected over the past 80 years, and identified twenty amphibian species belonging to seven families and twelve genera by morphology. Of these species, seven were listed in the threatened categories of the Red List of China\'s Biodiversity and thirteen were endemic to China. Ten species were found on the plateau side (western slope) and eleven species were found on the other side close to the Sichuan Basin (eastern slope). Only one species was found on both sides, indicating different community structures horizontally. The species richness was unimodal vertically and peaking at mid elevation on both sides, with the maximum number (ten vs. nine) of species occurring at 3300-3700 vs. 1700-1900 m a.s.l. and in different types of vegetation. The elevation span and body length of species distributed on both slopes did not show significant differences. These findings help to understand the horizontal and vertical distribution pattern of amphibian diversity, laying a foundation for future biogeographical and conservation research in this area.

In recent years, increased species extinction and habitat loss have significantly reduced biodiversity, posing a serious threat to both nature and human survival. Environmental factors strongly influence bird distribution and diversity. The potential distribution patterns and species richness offer a conservation modeling framework for policymakers to assess the effectiveness of natural protected areas (PAs) and optimize their existing ones. Very few such studies have been published that cover a large and complete taxonomic group with fine resolution at regional scale. Here, using birds as a study group, the maximum entropy model (MaxEnt) was used to analyze the pattern of bird species richness in Jiangsu Province. Using an unparalleled amount of occurrence data, we created species distribution models (SDMs) for 312 bird species to explore emerging diversity patterns at a resolution of 1 km2. The gradient of species richness is steep, decreasing sharply away from water bodies, particularly in the northern part of Jiangsu Province. The migratory status and feeding habits of birds also significantly influence the spatial distribution of avian species richness. This study reveals that the regions with high potential bird species richness are primarily distributed in three areas: the eastern coastal region, the surrounding area of the lower reaches of the Yangtze River, and the surrounding area of Taihu Lake. Compared with species richness hotspots and existing PAs, we found that the majority of hotspots are well-protected. However, only a small portion of the regions, such as coastal areas of Sheyang County in Yancheng City, as well as some regions along the Yangtze River in Nanjing and Zhenjiang, currently have relatively weak protection. Using stacked SDMs, our study reveals effective insights into diversity patterns, directly informing conservation policies and contributing to macroecological research advancements.

The species-area relationship is important for understanding species diversity patterns at spatial scales, but few studies have examined the relationship using environmental DNA (eDNA) techniques. We investigated amphibian diversity on 21 islands of the Zhoushan Archipelago and nearby mainland areas in China using the combination of eDNA metabarcoding and the traditional line transect method (TLTM) and identified the species-area relationship for amphibians on the islands. The mean detection probability of eDNA is 0.54, while the mean detection probability of TLTM is 0.24. The eDNA metabarcoding detected eight amphibian species on the islands and nine species in the mainland areas, compared with seven species on the islands and nine species in the mainland areas that were identified by TLTM. Amphibian richness on the islands increased with island area and habitat diversity. The species-area relationship for amphibians in the archipelago was formulated as the power function (S = 0.47A0.21) or exponential function (S = 2.59 + 2.41 (logA)). Our results suggested that eDNA metabarcoding is more sensitive for the detection of amphibian species. The combined use of eDNA metabarcoding and the traditional line transect method may optimize the survey results for amphibians.

Species richness plays an important role in ecosystem stability and health. Mycorrhizal type is an important factor affecting ecological processes. How mycorrhizal types affect understory herb species richness and their responses to environmental changes remain largely unknown. We investigated the effects of mycorrhizal types on species richness and their responses to environmental change in understory herbaceous communities based on data of three mycorrhizal types of dominated trees (including 1604 arbuscular mycorrhiza (AM) trees, 4654 ectomycorrhiza (ECM) trees, and 5568 AM+ECM trees) and environmental factors in America. The results showed significant differences in species richness of herbaceous plant communities among different mycorrhizal types. Forests with higher dominance of AM plants tended to have higher herbaceous plant richness, supporting the mycorrhizal mediation hypothesis. The impacts of environmental factors (latitude, temperature, precipitation, nitrogen deposition, and soil characteristics) on species richness of herbaceous plant communities depended on mycorrhizal type of forests. The species richness of understory herbs in AM, ECM, and AM+ECM forests was mostly affected by nitrogen deposition, temperature, and soil pH, with the relative importance of 42.3%, 41.1% and 48.7%, respectively. Mycorrhizal types of dominant trees played a vital role in regulating the species richness of understory herbs and influenced their responses to environmental changes.
物种丰富度对生态系统的稳定和健康有着重要意义,菌根类型是影响生态过程的一个重要因素,目前缺乏对菌根类型影响林下草本植物物种丰富度及其对环境变化响应的认识。本研究基于美国1604个丛枝菌根(AM)森林、4654个外生菌根(ECM)森林和5568个AM+ECM型森林的草本植物群落物种丰富度和环境因素数据,探讨菌根类型对物种丰富度及其对环境变化响应的影响。结果表明:不同菌根类型森林的草本植物群落物种丰富度间有显著差异,含有AM优势植物越多的森林的草本植物丰富度越高,这一结果为菌根介导假说提供了有力的证据。环境因子(纬度、温度、降水、氮沉降及土壤性状)对森林草本植物群落物种丰富度的影响也随菌根类型的不同而有着较大差异。在AM型、ECM型和AM+ECM型森林植被中,林下草本植物群落的物种丰富度分别受氮沉降、温度和土壤pH的影响最大,这些因素的相对重要性高达42.3%、41.1%和48.7%。森林优势植物的菌根类型在调节林下草本植物群落物种丰富度方面有着重要作用,且影响着群落物种丰富度对环境变化的响应。.

A total of 1,348 endophytic fungal strains were isolated from Ferula ovina, F. galbaniflua, and F. persica. They included Eurotiales (16 species), Pleosporales (11 species), Botryosphaeriales (1 species), Cladosporiales (2 species), Helotiales (6 species), Hypocreales (31 species), Sordariales (7 species), Glomerellales (2 species), and Polyporales (1 species). F. ovina had the richest species composition of endophytic fungi, and the endophytic fungi were most abundant in their roots compared to shoots. Chao, Margalef, Shannon, Simpson, Berger-Parker, Menhinick, and Camargo indices showed that F. ovina roots had the most endophytic fungal species. The frequency distribution of fungal species isolated from Ferula spp. fell into the log-series model, and F. ovina roots had the highest Fisher alpha. The dominance indices showed that there are no dominant species in the endophytic fungal community isolated from Ferula spp., indicating community stability. Evenness values were 0.69, 0.90, 0.94, and 0.57 for endophytic fungi isolated from F. ovina roots, F. ovina shoots, F. galbaniflua roots, and F. persica roots, respectively, indicating a species distribution that tends toward evenness. The fungal species community isolated from each of F. ovina roots, F. ovina shoots, F. galbaniflua roots, and F. persica roots was a diverse species group originating from a homogeneous habitat. Their distribution followed a log-normal distribution, suggesting that the interactions of numerous independent environmental factors multiplicatively control species abundances. Principal component analysis showed that the highest species diversity and dominance were observed in the endophytic fungal community isolated from F. ovina and F. persica roots, respectively.

Biocrusts are a prevalent form of living cover in worldwide drylands, and their presence are intimately associated with herbaceous community, forming a spatially mosaic distribution pattern in dryland ecosystems. The role of biocrusts as modulators of herbaceous community assembly is extensively studied, whereas, less is known whether their interactions are permanent or changeable with various environmental conditions. This study conducted a field survey of herbaceous community accompanied by three types of biocrusts (cyanobacterial, cyanobacterial-moss mixed, and moss crusts) in two contrasting (dry and wet) semiarid climate regions in the Chinese Loess Plateau, to explore whether or not climatic aridity gradient affects the interactions between biocrusts and herbaceous community. Our results showed that in dry semiarid climate, the biomass, species richness, and diversity of herbaceous community from biocrust plots were 89 %, 179 %, and 52 % higher than that from the uncrusted plots, respectively, while in wet semiarid climate, those herbaceous community indices from biocrust plots were 68 %, 43 %, and 23 % lower than that from the uncrusted plots, respectively. The impacts of biocrusts on herbaceous community were highly dependent on the types and coverage of biocrusts. Regardless of aridity gradient, the richness and diversity of herbaceous community were the lowest in the moss-covered plots, followed by the cyanobacteria-covered plots and the plots with a mixed cyanobacteria and moss population. Along with increasing biocrust coverage, the species richness and diversity of herbaceous plants initially increased and then decreased in dry semiarid climate, while in wet semiarid climate they decreased linearly with biocrust coverage. Structural equation modeling revealed that the factors of biocrust types and coverage affected herbaceous community indirectly through soil properties in dry semiarid climate, whereas in wet semiarid climate they directly affected herbaceous community through biotic interactions. Together, our findings indicated that cyanobacterial and moss biocrusts facilitate the development of herbaceous community in dry semiarid climate by increasing soil stability and nutrient levels, but in wet semiarid climate they restrict herbaceous plant growth through competing niche space. These results highlight the divergent relationships between biocrusts and herbaceous community across aridity gradient in dryland ecosystems, and this knowledge may be critically important in light of the projected global climate change which is going to change the aridity of global drylands.

Understanding the determinants of biodiversity in fragmented habitats is fundamental for informing sustainable landscape development, especially in urban landscapes that substantially fragment natural habitat. However, the relative roles of landscape and habitat characteristics, as emphasized by two competing frameworks (the island biogeography theory and the habitat diversity hypothesis), in structuring species assemblages in fragmented habitats have not been fully explored. This study investigated bird assemblages at 26 habitat patches (ranging in size from 0.3 to 290.4 ha) in an urban landscape, southwest China, among which habitat type composition and woody plant species composition varied significantly. Through 14 bird surveys conducted over six breeding seasons from 2017 to 2022, we recorded 70 breeding bird species (excluding birds recorded only once and fly-overs, such as raptors, swallows and swifts), with an average of 26 ± 10 (SD) species per patch. We found that patch area had significant direct and indirect effects on bird richness, with the indirect effects mediated by habitat richness (i.e., the number of habitat types). Isolation (measured as the distance to the nearest patch), perimeter to area ratio (PAR), and woody plant richness did not significantly predict variation in bird richness. Furthermore, none of these factors significantly sorted bird species based on their functional traits. However, the overall makeup of bird assemblages was significantly associated with the specific habitat types and woody plant species present in the patches. The results suggest that neither the island biogeography theory nor the habitat diversity hypothesis can fully explain the impacts of habitat fragmentation on bird richness in our study system, with their roles primarily being linked to patch area. The findings that habitat and plant compositions were the major drivers of variation in bird assemblage composition offer valuable insights into urban planning and green initiatives. Conservation efforts should focus not only on preserving large areas, but also on preventing urban monocultures by promoting diverse habitats within those areas, contributing to the persistence of meta-communities.

Higher biodiversity is often assumed to be a more desirable scenario for maintaining the functioning of ecosystems, but whether species-richer communities are also more disturbance-tolerant remains controversial. In this study, we investigated the bacterial communities based on 472 soil samples from 28 forests across China with associated edaphic and climatic properties. We developed two indexes (i.e., community mean tolerance breadth [CMTB] and community mean response asynchrony [CMRA]) to explore the relationship between diversity and community resistance potential. Moreover, we examined this resistance potential along the climatic and latitudinal gradients. We revealed that CMTB was significantly and negatively related to species richness, resulting from the changes in balance between relative abundances of putative specialists and generalists. In comparison, we found a unimodal relationship between CMRA and richness, suggesting that higher biodiversity might not always lead to higher community resistance. Moreover, our results showed differential local patterns along latitude. In particular, local patterns in the northern region mainly followed general relationships rather than those for the southern forests, which may be attributed to the differences in annual means and annual variations of climate conditions. Our findings highlight that the community resistance potential depends on the composition of diverse species with differential environmental tolerance and responses. This study provides a new, testable evaluation by considering tolerance breadth and response asynchrony at the community level, which will be helpful in assessing the influence of disturbance under rapid shifts in biodiversity and species composition as a result of global environmental change.