Microorganisms have a pivotal role in the functioning of ecosystems. Recent studies have shown that microbial communities harbour keystone taxa, which drive community composition and function irrespective of their abundance. In this Opinion article, we propose a definition of keystone taxa in microbial ecology and summarize over 200 microbial keystone taxa that have been identified in soil, plant and marine ecosystems, as well as in the human microbiome. We explore the importance of keystone taxa and keystone guilds for microbiome structure and functioning and discuss the factors that determine their distribution and activities.

Root-associated microbes play a key role in plant performance and productivity, making them important players in agroecosystems. So far, very few studies have assessed the impact of different farming systems on the root microbiota and it is still unclear whether agricultural intensification influences the structure and complexity of microbial communities. We investigated the impact of conventional, no-till, and organic farming on wheat root fungal communities using PacBio SMRT sequencing on samples collected from 60 farmlands in Switzerland. Organic farming harbored a much more complex fungal network with significantly higher connectivity than conventional and no-till farming systems. The abundance of keystone taxa was the highest under organic farming where agricultural intensification was the lowest. We also found a strong negative association (R2 = 0.366; P < 0.0001) between agricultural intensification and root fungal network connectivity. The occurrence of keystone taxa was best explained by soil phosphorus levels, bulk density, pH, and mycorrhizal colonization. The majority of keystone taxa are known to form arbuscular mycorrhizal associations with plants and belong to the orders Glomerales, Paraglomerales, and Diversisporales. Supporting this, the abundance of mycorrhizal fungi in roots and soils was also significantly higher under organic farming. To our knowledge, this is the first study to report mycorrhizal keystone taxa for agroecosystems, and we demonstrate that agricultural intensification reduces network complexity and the abundance of keystone taxa in the root microbiome.

Aridity, which is increasing worldwide because of climate change, affects the structure and functioning of dryland ecosystems. Whether aridification leads to gradual (versus abrupt) and systemic (versus specific) ecosystem changes is largely unknown. We investigated how 20 structural and functional ecosystem attributes respond to aridity in global drylands. Aridification led to systemic and abrupt changes in multiple ecosystem attributes. These changes occurred sequentially in three phases characterized by abrupt decays in plant productivity, soil fertility, and plant cover and richness at aridity values of 0.54, 0.7, and 0.8, respectively. More than 20% of the terrestrial surface will cross one or several of these thresholds by 2100, which calls for immediate actions to minimize the negative impacts of aridification on essential ecosystem services for the more than 2 billion people living in drylands.Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

Climate change is altering the frequency and severity of drought events. Recent evidence indicates that drought may produce legacy effects on soil microbial communities. However, it is unclear whether precedent drought events lead to ecological memory formation, i.e., the capacity of past events to influence current ecosystem response trajectories. Here, we utilize a long-term field experiment in a mountain grassland in central Austria with an experimental layout comparing 10 years of recurrent drought events to a single drought event and ambient conditions. We show that recurrent droughts increase the dissimilarity of microbial communities compared to control and single drought events, and enhance soil multifunctionality during drought (calculated via measurements of potential enzymatic activities, soil nutrients, microbial biomass stoichiometry and belowground net primary productivity). Our results indicate that soil microbial community composition changes in concert with its functioning, with consequences for soil processes. The formation of ecological memory in soil under recurrent drought may enhance the resilience of ecosystem functioning against future drought events.© 2021. The Author(s).

Soil microbial communities play a crucial role in ecosystem functioning, but it is unknown how co-occurrence networks within these communities respond to disturbances such as climate extremes. This represents an important knowledge gap because changes in microbial networks could have implications for their functioning and vulnerability to future disturbances. Here, we show in grassland mesocosms that drought promotes destabilising properties in soil bacterial, but not fungal, co-occurrence networks, and that changes in bacterial communities link more strongly to soil functioning during recovery than do changes in fungal communities. Moreover, we reveal that drought has a prolonged effect on bacterial communities and their co-occurrence networks via changes in vegetation composition and resultant reductions in soil moisture. Our results provide new insight in the mechanisms through which drought alters soil microbial communities with potential long-term consequences, including future plant community composition and the ability of aboveground and belowground communities to withstand future disturbances.

Despite the importance of microbial communities for ecosystem services and human welfare, the relationship between microbial diversity and multiple ecosystem functions and services (that is, multifunctionality) at the global scale has yet to be evaluated. Here we use two independent, large-scale databases with contrasting geographic coverage (from 78 global drylands and from 179 locations across Scotland, respectively), and report that soil microbial diversity positively relates to multifunctionality in terrestrial ecosystems. The direct positive effects of microbial diversity were maintained even when accounting simultaneously for multiple multifunctionality drivers (climate, soil abiotic factors and spatial predictors). Our findings provide empirical evidence that any loss in microbial diversity will likely reduce multifunctionality, negatively impacting the provision of services such as climate regulation, soil fertility and food and fibre production by terrestrial ecosystems.

Chimeric DNA sequences often form during polymerase chain reaction amplification, especially when sequencing single regions (e.g. 16S rRNA or fungal Internal Transcribed Spacer) to assess diversity or compare populations. Undetected chimeras may be misinterpreted as novel species, causing inflated estimates of diversity and spurious inferences of differences between populations. Detection and removal of chimeras is therefore of critical importance in such experiments.We describe UCHIME, a new program that detects chimeric sequences with two or more segments. UCHIME either uses a database of chimera-free sequences or detects chimeras de novo by exploiting abundance data. UCHIME has better sensitivity than ChimeraSlayer (previously the most sensitive database method), especially with short, noisy sequences. In testing on artificial bacterial communities with known composition, UCHIME de novo sensitivity is shown to be comparable to Perseus. UCHIME is >100× faster than Perseus and >1000× faster than ChimeraSlayer.robert@drive5.comSource, binaries and data: http://drive5.com/uchime.Supplementary data are available at Bioinformatics online.

Relationships between biodiversity and multiple ecosystem functions (that is, ecosystem multifunctionality) are context-dependent. Both plant and soil microbial diversity have been reported to regulate ecosystem multifunctionality, but how their relative importance varies along environmental gradients remains poorly understood. Here, we relate plant and microbial diversity to soil multifunctionality across 130 dryland sites along a 4,000 km aridity gradient in northern China. Our results show a strong positive association between plant species richness and soil multifunctionality in less arid regions, whereas microbial diversity, in particular of fungi, is positively associated with multifunctionality in more arid regions. This shift in the relationships between plant or microbial diversity and soil multifunctionality occur at an aridity level of ∼0.8, the boundary between semiarid and arid climates, which is predicted to advance geographically ∼28% by the end of the current century. Our study highlights that biodiversity loss of plants and soil microorganisms may have especially strong consequences under low and high aridity conditions, respectively, which calls for climate-specific biodiversity conservation strategies to mitigate the effects of aridification.© 2021. The Author(s).

Drylands are home to more than 38% of the total global population and are one of the most sensitive areas to climate change and human activities(1,2). Projecting the areal change in drylands is essential for taking early action to prevent the aggravation of global desertification(3,4). However, dryland expansion has been underestimated in the Fifth Coupled Model Intercomparison Project (CMIP5) simulations(5) considering the past 58 years (1948-2005). Here, using historical data to bias-correct CMIP5 projections, we show an increase in dryland expansion rate resulting in the drylands covering half of the global land surface by the end of this century. Dryland area, projected under representative concentration pathways (RCPs) RCP8.5 and RCP4.5, will increase by 23% and 11%, respectively, relative to 1961-1990 baseline, equalling 56% and 50%, respectively, of total land surface. Such an expansion of drylands would lead to reduced carbon sequestration and enhanced regional warming(6,7), resulting in warming trends over the present drylands that are double those over humid regions. The increasing aridity, enhanced warming and rapidly growing human population will exacerbate the risk of land degradation and desertification in the near future in the drylands of developing countries, where 78% of dryland expansion and 50% of the population growth will occur under RCP8.5.

Background & Aims: Global change and other human activities are changing biodiversity around the world at an unprecedented rate, which has led to a sharp decline in global biodiversity and productivity, an increase in pests and diseases, and a weakening of the ability to resist invasion and other ecological problems. Ecologists became more and more interested in the question of whether and how the continuous loss of biodiversity would affect ecosystem functioning in the last 30 years. Therefore, the relationship between biodiversity and ecosystem functioning (BEF) became one of the hot topics of ecological research. For a long time, researchers have focused more on individual ecosystem functions than on the ability of an ecosystem to provide multiple ecosystem functions at the same time, known as ecosystem multifunctionality (EMF). Considering only individual functions could underestimate the impact of biodiversity on overall ecosystem functioning. Therefore, the relationship between biodiversity and ecosystem multifunctionality (BEMF) has become the focus of BEF research field. In order to enrich the understanding of BEMF relationships, this paper focuses on different dimensions of biodiversity and the impact of microbial diversity on EMF, how abiotic factors drive EMF, as well as the selection of functional indicators in the evaluation of EMF. Progresses: In recent years, the research on BEMF relationships has developed rapidly, expanding from aquatic ecosystems to grasslands, forests, drylands and agricultural ecosystems. Spatial scale ranges from regional scale to global scale. The driving mechanisms of BEMF relationship are explored from single dominant driving mechanism to multiple driving mechanisms. There are also new innovations in research methods and new concepts put forward. Prospects: However, there are still some shortcomings. For example, there is no unified standard for the selection of functional indicators in EMF research, insufficient attention to microbial diversity, few studies on the BEMF relationship at the multitrophic level, and debate about the mechanisms driving EMF. In the future, it is necessary to strengthen the research on the criteria for the selection of functional indicators, comprehensively analyze the overall impact of aboveground and belowground biodiversity and abiotic factors on EMF, and strengthen the research and application of ecosystem multiserviceability (EMS).

全球变化和人类活动正以空前的速度在世界范围内改变着生物多样性, 这导致了全球生物多样性的锐减以及生产力的下降、病虫害的增加和抗入侵能力的减弱等生态问题。近30年来, 生态学家开始对于生物多样性的持续丧失是否以及如何影响生态系统功能的问题越来越感兴趣, 生物多样性与生态系统功能(biodiversity and ecosystem functioning, BEF)关系的研究应运而生, 并成为生态学研究的热点之一。但长期以来, 研究者更多地关注单一生态系统功能, 而忽略了生态系统能够同时提供多种生态系统功能的能力, 即生态系统多功能性(ecosystem multifunctionality, EMF)。本文综述了EMF研究中功能指标的选择、生物多样性的不同维度、微生物多样性对EMF的影响以及其他非生物因子对EMF的驱动等进展。因只考虑单一功能可能会低估生物多样性对整体生态系统功能的影响, 故生物多样性与生态系统多功能性(BEMF)关系的研究成为BEF关系研究的重点。近年来, BEMF关系的研究发展较快, 在不同生态系统(包括水生、草地、森林、旱地、农业等)、不同研究尺度(从区域到全球尺度)、BEMF关系的驱动机制(从单一驱动机制到多种驱动机制共同作用)、研究方法(包括新概念以及新的量化方法的提出和应用)等方面均取得了新的进展。但仍有不足之处, 如对于EMF研究中功能指标的选取没有统一的标准、对地下微生物多样性的关注度不够、涉及多营养级水平下的BEMF关系研究较少、驱动EMF的机制仍存在争论等。未来应加强对于功能指标选取的标准研究, 综合分析地上、地下生物多样性以及非生物因子对EMF的整体影响, 加强生态系统多服务性(ecosystem multiserviceability, EMS)方法的研究和应用。

<p id="p00005"><strong>Aims:</strong> During the first two decades of the 21st century, China has made remarkable progress in desertification control. The area of desertified and degraded grassland has been decreasing and the amount of vegetation has been increasing. However, it remains unclear how plant diversity varies during vegetation restoration. This knowledge gap hinders a full assessment of the effectiveness of desertification control efforts. Our goal was to quantify species diversity, functional diversity, and phylogenetic diversity in plant communities at different phases of vegetation restoration (semi-fixed dunes, fixed dunes, fixed dunes covered with biological soil crusts, fixed dunes with abundant herbaceous plants) in the Mu Us sandy grassland.</p> <p id="p00010"><strong>Methods:</strong> We conducted field investigations and leaf trait measurements (leaf thickness, leaf dry matter content, leaf density, and specific leaf area) during the mid-growing season of 2020 in Yanchi, Ningxia. Based on this, we further used one-way ANOVA and Pearson correlation analysis to explore the differences and relationships among diversity indices at different phases of vegetation restoration.</p> <p id="p00015"><strong>Results:</strong> Our results indicated that: (1) Most leaf traits exhibited no significant phylogenetic signal, implying that leaf functional traits were primarily driven by environmental factors. (2) For &#x003b1;-diversity, Shannon-Wiener diversity (<i>H</i>), species richness (<i>S</i>), functional richness (<i>FRic</i>), and phylogenetic diversity (<i>PD</i>) were the lowest in plant communities at the phase of fixed dunes covered with biological soil crusts. Each of these &#x003b1;-diversity parameters were not significantly different among plant communities during the other three restoration phases. Furthermore, these biodiversity indices were positively correlated with each other, suggesting coordinated changes in species diversity, functional diversity, and phylogenetic diversity during vegetation restoration. (3) All &#x003b2;-diversity indices increased with the number of transitions between phases, indicating that species composition, leaf traits, and phylogeny were consistently changing during vegetation restoration. Species composition, leaf traits, and phylogeny all changed dramatically during the transition from semi-fixed to fixed dunes, resulting in a large dissimilarity between communities during the two phases. (4) The phylogenetic structure of plant communities tended to diverge on fixed dunes, fixed dunes covered with biological soil crusts, and fixed dunes with abundant herbaceous plants, indicating that competitive exclusion was the key factor driving community organization. However, the phylogenetic structure of plant communities on semi-fixed dunes did not exhibit any consistent patterns, implying that community organization was affected by the combined effects of habitat filtering and competitive exclusion.</p> <p id="p00020"><strong>Conclusion:</strong> Although plant diversity did not demonstrate a monotonic increasing trend during vegetation restoration in the Mu Us sandy grassland, different indices of diversity varied coordinately. Therefore, species diversity can be regarded as a reasonable proxy of functional and phylogenetic diversity in this system. The results of this study can provide reference for vegetation construction and management whilst implementing desertification controls, as well as provide scientific basis for the ecological conservation and biodiversity protection of the Mu Us sandy grassland.</p>

进入21世纪以来, 中国荒漠化恢复取得显著成效, 荒漠化、沙化土地面积持续减少, 植被覆盖度大幅提升, 但关于植被恢复过程中生物多样性如何变化的研究不足, 这制约着对荒漠化恢复成效的全面评估。本文基于群落调查和叶功能性状(叶片厚度、叶片干物质含量、比叶面积和叶片密度)的测定, 分析了毛乌素沙地不同恢复阶段(半固定沙地、固定沙地、结皮覆盖沙地和草本植物覆盖沙地)的植物群落物种多样性、功能多样性和系统发育多样性特征。结果表明: (1)多数叶功能性状的系统发育信号不显著, 表明环境因子对研究区植物功能性状的塑造作用很强。(2)对于&#x003b1;多样性, 结皮覆盖沙地的物种多样性(Shannon-Wiener多样性, H)、物种丰富度(S)、功能丰富度(FRic)及系统发育多样性(PD)指数均显著低于其他恢复阶段, 而其他3个阶段间无显著差异; 这些指数间均显著正相关, 表明物种多样性、功能多样性和系统发育多样性在植被恢复过程中协同变化。(3) &#x003b2;多样性指数随恢复阶段间隔增加而逐渐增大, 表明物种组成、功能属性及系统发育关系随植被恢复持续变化, 且半固定沙地到固定沙地的群落物种组成、功能属性及系统发育关系更替最快, 导致群落间差异最大。(4)固定沙地、结皮覆盖沙地和草本植物覆盖沙地群落系统发育结构均趋向于发散, 表明竞争排斥是群落构建的主要驱动力; 而半固定沙地群落系统发育结构无一致规律, 表明群落构建可能受到生境过滤和竞争排斥的综合作用。研究结果可为植被建设与管理提供参考, 为毛乌素沙地生态保育和生物多样性的保护提供科学依据。

Loss in plant diversity is expected to impact biodiversity and ecosystem functioning (BEF) in terrestrial ecosystems. Soil microbes play essential roles in regulating ecosystem functions. However, the important roles and differences in bacterial and fungal diversity and rare microbial taxa in driving soil multifunctionality based on plant diversity remain poorly understood in grassland ecosystems. Here, we carried out an experiment in six study sites with varied plant diversity levels to evaluate the relationships between soil bacterial and fungal diversity, rare taxa, and soil multifunctionality in a semi-arid grassland. We used Illumina HiSeq sequencing to determine soil bacterial and fungal diversity and evaluated soil functions associated with the nutrient cycle. We found that high diversity plant assemblages had a higher ratio of below-ground biomass to above-ground biomass, soil multifunctionality, and lower microbial carbon limitation than those with low diversity. Moreover, the fungal richness was negatively and significantly associated with microbial carbon limitations. The fungal richness was positively related to soil multifunctionality, but the bacterial richness was not. We also found that the relative abundance of saprotrophs was positively correlated with soil multifunctionality, and the relative abundance of pathogens was negatively correlated with soil multifunctionality. In addition, the rare fungal taxa played a disproportionate role in regulating soil multifunctionality. Structural equation modeling showed that the shift of plant biomass allocation patterns increased plant below-ground biomass in the highly diverse plant plots, which can alleviate soil microbial carbon limitations and enhance the fungal richness, thus promoting soil multifunctionality. Overall, these findings expand our comprehensive understanding of the critical role of soil fungal diversity and rare taxa in regulating soil multifunctionality under global plant diversity loss scenarios.

While it is well established that species composition affects ecosystem function, the way in which species combine to control overall ecosystem functioning is still debated. In experimental mesocosms, we planted three functionally distinct dry-heath species in varying proportions and measured multiple ecosystem properties related to nutrient cycling and carbon storage (hereafter functions). Overall ecosystem functioning was described as the main axes of variation in ecosystem functioning (functional space) and the proportion of ecosystem functions at high levels, e.g. fast carbon and nutrient cycling (cluster-based multifunctionality). The first functional space axis, related to nitrogen availability, was driven by plant species abundance, particularly that of the legume, which strongly affected many individual functions. The second, related to total plant biomass and woodiness, was mostly driven by the abundance of the dwarf shrub. Similarly, cluster-based multifunctionality was related to the initial abundance of all species, but particularly the legume. Interactions between species also affected ecosystem multifunctionality, but these effects were smaller in magnitude. These results indicate that species interactions could play a secondary role to species abundance and identity in driving the overall ecosystem functioning of heathlands, but also that axes of variation in functional space are clearly linked to plant functional composition.This article is protected by copyright. All rights reserved.

While soil erosion drives land degradation, the impact of erosion on soil microbial communities and multiple soil functions remains unclear. This hinders our ability to assess the true impact of erosion on soil ecosystem services and our ability to restore eroded environments. Here we examined the effect of erosion on microbial communities at two sites with contrasting soil texture and climates. Eroded plots had lower microbial network complexity, fewer microbial taxa, and fewer associations among microbial taxa, relative to non-eroded plots. Soil erosion also shifted microbial community composition, with decreased relative abundances of dominant phyla such as Proteobacteria, Bacteroidetes, and Gemmatimonadetes. In contrast, erosion led to an increase in the relative abundances of some bacterial families involved in N cycling, such as Acetobacteraceae and Beijerinckiaceae. Changes in microbiota characteristics were strongly related with erosion-induced changes in soil multifunctionality. Together, these results demonstrate that soil erosion has a significant negative impact on soil microbial diversity and functionality.

Phylogenetic diversity (PD) describes the total amount of phylogenetic distance among species in a community. Although there has been substantial research on the factors that determine community PD, exploration of the consequences of PD for ecosystem functioning is just beginning. We argue that PD may be useful in predicting ecosystem functions in a range of communities, from single-trophic to complex networks. Many traits show a phylogenetic signal, suggesting that PD can estimate the functional trait space of a community, and thus ecosystem functioning. Phylogeny also determines interactions among species, and so could help predict how extinctions cascade through ecological networks and thus impact ecosystem functions. Although the initial evidence available suggests patterns consistent with these predictions, we caution that the utility of PD depends critically on the strength of phylogenetic signals to both traits and interactions. We advocate for a synthetic approach that incorporates a deeper understanding of how traits and interactions are shaped by evolution, and outline key areas for future research. If these complexities can be incorporated into future studies, relationships between PD and ecosystem function bear promise in conceptually unifying evolutionary biology with ecosystem ecology.© 2012 Blackwell Publishing Ltd/CNRS.

植物的资源分配模式可以反映植物对环境的生态适应策略。本研究以毛乌素沙地优势半灌木油蒿（Artemisia ordosica）为研究对象，通过样地调查法，系统分析了不同沙漠化程度（潜在、轻度、中度、重度）下油蒿营养、生殖器官的生长特征和生物量分配规律。结果表明：（1）随着沙漠化程度的加剧，单位面积油蒿种群密度及地上生物量降低，枯死率增加。（2）沙漠化程度的加剧会促进油蒿个体的生长，其当年单株地上总生物量由374.4 g（潜在）增加至2 999.6 g（重度），增幅高达701.18%；这一过程中油蒿繁殖分配明显增加，营养分配显著降低（P&lt;0.05），潜在、轻度沙漠化阶段油蒿繁殖分配均保持在18.6%左右，增加不显著（P&gt;0.05），但中度、重度沙漠化阶段油蒿繁殖分配达到40.6%和62.4%，远高于潜在沙漠化阶段。（3）油蒿营养枝和生殖枝的直径、长度及生物量均随着沙漠化程度的增加而增加，但轻度沙漠化阶段油蒿营养枝的生物量显著大于（P&lt;0.05）潜在、中度沙漠化阶段，约是两者的2.0倍和0.7倍。（4）面对沙漠化程度的加剧，油蒿营养枝和生殖枝构件的各指标（叶生物量、茎生物量、穗生物量、叶密度和穗密度）整体上均呈增加趋势，但油蒿叶分配所占比重显著降低（P&lt;0.05），茎分配所占比重先增加后降低，轻度沙漠化阶段油蒿营养生长的茎分配占比最大（41.1%），而生殖枝构件中穗（种子）分配所占比重不断增加。因此，沙漠化的发展严重影响油蒿种群的生存和发展，但油蒿个体的生长及生物量分配格局会随着沙漠化程度的加剧发生调整与权衡，油蒿个体生长策略由以营养生长为主向生殖生长为主发生转变。

Our understanding of how biodiversity influences ecosystem functioning is entering a new stage of its development through the incorporation of information about the evolutionary relatedness of species. Bacteria are prime providers of essential ecosystem services, representing an excellent model system to perform biodiversity-ecosystem function research. By using bacteria isolated from petroleum-contaminated sites, we show that communities composed of poorly related species were more productive than those containing highly related species. The nature of the forces controlling this positive effect of phylogenetic diversity on community productivity depended on the number of species in culture. In communities of two species the positive effect of phylogenetic diversity on productivity was driven by changes in the selection effect. Communities of two distantly related species were dominated by the most productive species in monoculture, whereas communities of two closely related species were dominated by the less productive species in monoculture. In communities of four species the positive effect of phylogenetic diversity on productivity was driven by changes in the complementarity effect. In communities composed of four distantly related species the influence of positive interactions such as facilitation, cross-feeding, and niche partitioning seemed to outweigh the influence of negative interactions such as interference. As a consequence the proportion of species favored by the presence of other species increased as they became less related. Multiple facets of biodiversity may influence ecosystem functioning. Here, we present evidence of an interaction between phylogenetic and taxonomic diversity on community productivity, underlining the importance of considering multiple aspects of biodiversity when studying its impact on ecosystem functioning.

The soil microbiome is highly diverse and comprises up to one quarter of Earth's diversity. Yet, how such a diverse and functionally complex microbiome influences ecosystem functioning remains unclear. Here we manipulated the soil microbiome in experimental grassland ecosystems and observed that microbiome diversity and microbial network complexity positively influenced multiple ecosystem functions related to nutrient cycling (e.g. multifunctionality). Grassland microcosms with poorly developed microbial networks and reduced microbial richness had the lowest multifunctionality due to fewer taxa present that support the same function (redundancy) and lower diversity of taxa that support different functions (reduced  functional uniqueness). Moreover, different microbial taxa explained different ecosystem functions pointing to the significance of functional diversity in microbial communities. These findings indicate the importance of microbial interactions within and among fungal and bacterial communities for enhancing ecosystem performance and demonstrate that the extinction of complex ecological associations belowground can impair ecosystem functioning.

Because of the correlation expected between the phylogenetic relatedness of two taxa and their net ecological similarity, a measure of the overall phylogenetic relatedness of a community of interacting organisms can be used to investigate the contemporary ecological processes that structure community composition. I describe two indices that use the number of nodes that separate taxa on a phylogeny as a measure of their phylogenetic relatedness. As an example of the use of these indices in community analysis, I compared the mean observed net relatedness of trees (≥10 cm diameter at breast height) in each of 28 plots (each 0.16 ha) in a Bornean rain forest with the net relatedness expected if species were drawn randomly from the species pool (of the 324 species in the 28 plots), using a supertree that I assembled from published sources. I found that the species in plots were more phylogenetically related than expected by chance, a result that was insensitive to various modifications to the basic methodology. I tentatively infer that variation in habitat among plots causes ecologically more similar species to co-occur within plots. Finally, I suggest a range of applications for phylogenetic relatedness measures in community analysis.

<p id="p00005"><strong>Aims</strong> Extreme drought exacerbates the expansion of desert areas around the world. Microbial diversity is associated with multiple ecosystem functions in the desert. Evaluating the response of fungal communities to extreme drought is essential for our understanding of regional desertification caused by drought in a temperate desert.</p><p id="p00010"><strong>Methods</strong> Based on three-year (D3) and ten-year (D10) drought plots established in the Gurbantunggut Desert, we investigated the effect of extreme drought on the diversity and ecological network of fungal communities.</p><p id="p00015"><strong>Results</strong> Our results demonstrated that in both the D3 and D10 plots, the droughts had no significant influence on the Chao1 and Shannon diversity indexes of the whole and abundant fungi, while the rare fungal Shannon diversity index significantly increased. Both extreme drought treatments had a noticeable effect on community composition of whole, abundant and rare fungi, with stronger effect on rare fungi (ANOSIM, <i>R</i> = 0.378-0.595, <i>P</i> &lt; 0.01) than that on the abundant fungi (ANOSIM, <i>R</i> = 0.282-0.555, <i>P</i> &lt; 0.01), suggesting that abundant fungi were more resistant to drought than rare taxa. Moreover, beta-diversity of the whole, abundant, and rare fungi decreased significantly in D3 and D10 treatments, suggesting that extreme drought served as an ecological filter on fungal community assembly. Molecular ecological network analysis revealed that in both the D3 and D10 plots there was a reduced fungal network complexity, suggesting that extreme drought reduced the interactions among fungal communities. In addition, abundant fungi had higher node topological parameters (<i>P</i> &lt; 0.05), indicating that abundant fungi were important for maintaining fungal species interactions under extreme drought conditions.</p><p id="p00020"><strong>Conclusion</strong> Extreme drought significantly altered fungal community composition and weakened the interactions among fungal communities in a temperate desert. Furthermore, rare fungi were sensitive to extreme drought, contributing to reducing the lag in the response to fungal communities, and abundant fungi, as the core microflora in fungal networks, were crucial to sustaining the stability of fungal communities and interactions among species under extreme drought conditions.</p>

评估极端干旱对温带荒漠土壤真菌群落的影响有助于进一步认识干旱导致的区域荒漠化特征。本研究利用在古尔班通古特沙漠建立的干旱三年和干旱十年样地, 分析了长期极端干旱对温带荒漠土壤真菌群落和生态网络的影响。结果显示, 干旱三年与干旱十年处理对总真菌和丰富真菌的Chao1和Shannon多样性指数均无显著性影响, 而对稀有真菌的Shannon多样性指数有显著促进作用; 干旱三年和干旱十年处理显著影响总真菌、丰富和稀有真菌的群落组成, 且极端干旱对稀有真菌群落变异的影响(ANOSIM, R = 0.378-0.595, P &lt; 0.01)大于对丰富真菌的影响(ANOSIM, R = 0.282-0.555, P &lt; 0.01), 表明丰富真菌具有更强的干旱抵抗力; 另外, 极端干旱显著降低了总真菌、丰富和稀有真菌的&#x003b2;多样性, 表明极端干旱具有生态过滤作用。分子生态网络结果显示, 干旱三年与干旱十年处理降低了荒漠土壤真菌群落网络复杂性, 表明极端干旱减弱了真菌物种间的相互作用; 相比稀有真菌, 丰富真菌具有更高的节点拓扑参数(P &lt; 0.05), 表明丰富真菌对维持极端干旱下的真菌物种间相互作用的重要性。综上所述, 极端干旱显著改变了荒漠表层土壤真菌群落组成, 减弱了真菌物种间的相互作用; 稀有真菌敏感响应极端干旱, 有利于减缓荒漠土壤真菌群落响应的滞后性; 丰富真菌作为网络的核心菌群, 对维持极端干旱下的真菌群落稳定性以及物种间的相互作用很关键。

In order to discuss the effects of vegetation restoration on soil nutrient status, the variation characteristics of soil nutrients among 5 different vegetation restoration types (natural grassland, enclosed grassland, abandoned land, land as returning farmland to woodland, fixed sandy land) on soil nutrient status were studied in southern edge of Mu Us sandy land. The results showed that: the influence of different vegetation restoration types on soil organic matter, total nitrogen, available nitrogen and available phosphorus were conspicuously different. The contents of soil organic matter, total nitrogen and available nitrogen in these lands (enclosed grassland, land as returning farmland to woodland and fixed sandy land) which were the combination of shrub and herb, were higher than in those lands (natural grassland and abandoned land) with mainly herb. But just the opposite, the contents of soil available phosphorus in these were lower than in those. The influence of vegetation on the surface 0-20 cm soil nutrient was greater than that on the deep 20-60 cm soil, also the soil nutrient was to surface enrichment under the action of vegetation. Planting the species (Caragana korshinskii) for converting cropland to forest could give full play to its root system characteristics, which could be helpful for improving deeper soil nutrient.

地表枯落物是毛乌素沙地生态系统的重要组成部分，风蚀是影响枯落物蓄积量及再分配的重要因素。采用野外调查采样与室内人工模拟风洞试验相结合的研究方法，分析了沙柳（Salix psammophila）群落枯落物组分特征及其对土壤风蚀的影响。结果表明：（1）沙柳枯落物地表物质组成中枝和叶占比分别为56%和30%，且随着距沙柳基部距离的增大，枯落物量呈显著减小趋势；（2）随着沙柳枯落物量的增加，土壤流失量呈指数函数递减趋势，且以处理400 g·m^-2为临界值；（3）与叶相比，沙柳群落枯落物的枝部分在抗风蚀方面起着主导作用。

The composition of tree species might influence microbial diversity considerably, yet investigation of the consequences of changes in diversity for stability of the microbial community is still in its early stages. Understanding how diversity governs community stability is vital for predicting the response of an ecosystem to environmental changes. Phylogenetic diversity (PD) describes the distinct evolution of species in a community, and might be useful for estimating the effects of biodiversity on ecosystem function and stability. High-throughput 16S rRNA gene sequencing was used to examine soil bacterial phylogenetic distances, phylogenetic diversity and interactions between individuals in five single-species plantations and three mixed-species plantations. The plantations were established on the same initial substrate, and sampling was at 68 relatively spatially independent sites. Our results showed that mixed tree species enhanced soil bacterial phylogenetic diversity and community stability, and that phylogenetic diversity had a positive effect on stability of the soil microbial community. We also found evidence that microbial communities characterized by distantly related species with weak interactions were more stable in mixed plantations than communities with strong interactions in single-species plantations. These results may be explained by the "insurance hypothesis", that large phylogenetic diversity of microbial communities, which share different ecological niches, insures them against decline in their stability. This is because, even if some microbial species fail to deal with environmental change, others might not necessarily be affected similarly. Our findings demonstrate that phylogenetic diversity is the main controlling factor of the variation in stability across sites and requires more attention in sustainable forest management.