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Aim: Understanding how species' traits mediate environmental responses provides a mechanistic perspective on community assembly processes. Although traits that influence the response of multicellular organisms to environments have been studied, the identification of such traits in unicellular organisms, like ciliates, is underexplored. Since ciliates are dominant animals in coastal sandy sediments and contribute significantly to interstitial community respiration, identifying links between their occurrence and sandy‐coast characteristics is crucial for conserving biodiversity and protecting coastal habitats. Location: Coasts of China. Methods: We used Hierarchical Modelling of Species Communities, a trait‐based joint species distribution model, to analyse ciliate community data collected from 344 sites belonging to 31 beaches across the Chinese coastline. Results: We found that physical variables play the most important role in determining ciliate occurrence. The beach index combines the tidal range, sediment grain size and beach slope of beach‐selected species based on body size as well as feeding type, while sediment grain size constrained different mobility types, with swimming species favouring fine sandy sediments. The significant contribution of phylogeny in explaining the residual variation among species responses indicates that there are phylogenetically conserved but unmeasured traits too that influence species' responses. Species richness of benthic ciliates was higher in dissipative beaches with high primary productivity. Main Conclusions: Based on our research, ciliate occurrence in coastal beaches is mediated by their traits which are filtered by local environmental variables. The beach index is essential in predicting distribution patterns and species richness of benthic ciliates. Nevertheless, further research is needed to identify additional traits that will enhance the accuracy of predicting ciliate niches. Our study provides insights into the mechanisms driving ciliate community assembly processes and has implications for the conservation of biodiversity in sandy coastal habitats. [ABSTRACT FROM AUTHOR]

Aim: Understanding large‐scale spatial distribution patterns is not only a central goal of ecology but is also essential for conservation planning. Nevertheless, the biogeographical patterns of diversity and composition remain unclear for microorganisms and the role of various factors in structuring their assemblages is still poorly known. Here, we tested whether the diversity and community structure of ciliates are driven by both local environmental and regional dispersal‐related processes. Location: Coasts of China. Taxon: Benthic ciliates. Methods: We sampled ciliates at 30 sandy beaches covering a latitudinal range of over 2500 km from October to November 2020. We first used generalized linear models to examine the most important predictors of ciliate alpha diversity. Then, distance‐based linear models (DistLM) were used to identify the relative importance of local and regional variables in explaining community structure variability. We further used nonmetric multidimensional scaling (NMDS) and permutational multivariate analysis of variance (PERMANOVA) to reveal patterns in community structure. Results: We found that local environmental factors including beach index (BI), salinity and mean particle size (MPS) were more important in shaping ciliate alpha diversity than latitude. However, the Shannon alpha diversity index decreased with latitude, perhaps due to anthropogenic disturbances. DistLM analysis emphasized regional processes in shaping community structure. Both NMDS and PERMANOVA supported a clear separation among the three clusters matching with the ecoregional delineations suggested for macroorganisms. We also note that community trait composition was partially explained by a local factor, i.e. the maximum spring tide range of beaches. Main conclusions: Ciliate communities were driven by both local environmental and regional factors. We suggest that these biogeographic patterns may have stemmed from large‐scale environmental filtering related to the outflow of Yangtze River, rather than from dispersal limitation or historical events. The current study provides a new understanding of the biogeographic patterns and underlying mechanisms of marine microorganisms, thus helping improve their management and conservation in the face of future global change. [ABSTRACT FROM AUTHOR]

Comparing spatio-temporal patterns between planktonic and benthic algae is helpful for understanding their associations and differences. However, such studies are still rare especially in large rivers. We used a dataset collected in the upper reach of the Jinsha River in different seasons to explore biodiversity and assembly processes of planktonic and benthic diatom assemblages. We found that planktonic and benthic diatoms presented different seasonal variation in species richness and community compositions. We also found evidence that planktonic and benthic diatoms were coupled in the summer. Planktonic diatom assemblages were mainly affected by spatial processes via directional spatial dispersal, especially in the summer. By comparison, benthic diatom assemblages were more affected by environmental processes. Our findings suggest that mass effect and species sorting paradigms explain the assembly processes of planktonic and benthic diatom assemblages, respectively, but the explanatory powers of these two paradigms vary seasonally. To effectively monitor and assess ecological conditions of large rivers, we recommend using benthic algae as a biotic indicator group as they had stronger correlations with environmental factors. [ABSTRACT FROM AUTHOR]

Aim: Many studies have found that diazotrophic distribution is mainly determined by soil properties from field to regional scales. However, we lack strong evidence for the relative importance of different drivers controlling broad‐scale biogeography of forest diazotrophs, especially for soil multi‐nutrients. Location: China's forests. Time period: 2012−2013. Major taxa studied: Diazotrophic communities. Methods: We investigated the distribution of soil diazotrophic communities from 146 sites along a 3,900‐km south–north transect by sequencing N‐fixing nifH gene amplicons. The relative contributions of environmental variables were assessed using a combination of stepwise multiple regression, variation partitioning analysis, multiple regression on distance matrices and partial least squares path modelling. Results: Overall, aridity index and temperature were the predominant parameters governing diazotrophic community diversity and structure, mainly through their indirect effects on soil pH, nutrient contents and plant productivity. Although soil multi‐nutrients (Ca, Mg, Fe, Mn, Na, Cu and Zn) were included in the statistical analysis, they still exhibited lower impacts on diazotrophic communities than climate. Intriguingly, the microelement Mo could not explain the diazotrophic community patterns, despite its significance in nitrogenase enzymes. This unexpected phenomenon was attributed to the relatively high Mo supply in our work. Moreover, the distinct responses of diazotroph taxa to climatic factors and large heterogeneity of diazotrophic diversity among forests in different climatic zones further support the dominant role of climatic variation. These results indicate the presence of differentiated climatic niches for diazotrophs, such as warm‐adapted Bradyrhizobium and cool‐adapted Azospirillum. Main conclusions: Our findings suggest for the first time that unlike prior studies, the key roles of soil nutrient limitation (even for Mo) and pH‐dependent mechanisms in small‐scale diazotrophic communities can be surpassed by large‐scale climatic gradients. Future changes in drought severity and temperature might greatly shape diazotrophic distribution and its potential function in forest N2 fixation. [ABSTRACT FROM AUTHOR]

Aim: Idealized metacommunity structures (i.e. checkerboard, random, quasi‐structures, nested, Clementsian, Gleasonian and evenly spaced) have recently gained increasing attention, but their relationships with environmental heterogeneity and how they vary with organism groups remain poorly understood. Here, we tested two main hypotheses: (a) gradient‐driven patterns (Clementsian and Gleasonian) occur frequently in heterogeneous environments and (b) small organisms (here, diatoms) are more likely to exhibit gradient‐driven patterns than large organisms (here, macroinvertebrates). Location: Streams in three regions in China. Taxon: Diatoms and macroinvertebrates. Methods: The stream diatom and macroinvertebrate data, as well as the environmental data collected from the same set of sites were used to examine the idealized metacommunity structures via the elements of the metacommunity structure (EMS; coherence, turnover and boundary clumping) analysis in three regions. We extended the traditional EMS approach by ordering sites along known environmental gradients. Results: We found that Clementsian structure with high degrees of coherence and turnover, and significantly positive clumping was typically observed in the high‐heterogeneity regions, whereas randomness was prevalent in the low‐heterogeneity region. Macroinvertebrates exhibited clearer Clementsian structures compared with diatoms, while diatoms showed more randomness compared with macroinvertebrates, indicating a stronger role of environmental filtering for macroinvertebrates than diatoms. In most cases, the results of the more novel EMS approach differed from the results of the traditional EMS technique. Main conclusions: Our results suggested that the occurrence of different metacommunity structures may be related with the degree of regional environmental heterogeneity. However, diatom metacommunities were more random than those of macroinvertebrate, and such an unexpected result may result from different dispersal abilities between the two organism groups. In addition, we found that the novel EMS approach increased power in discerning metacommunity structure in comparison to the traditional EMS technique. [ABSTRACT FROM AUTHOR]

A major challenge in community ecology is to understand the underlying factors driving metacommunity (i.e., a set of local communities connected through species dispersal) dynamics. However, little is known about the effects of varying spatial scale on the relative importance of environmental and spatial (i.e., dispersal related) factors in shaping metacommunities and on the relevance of different dispersal pathways. Using a hierarchy of insect metacommunities at three spatial scales (a small, within‐stream scale, intermediate, among‐stream scale, and large, among‐sub‐basin scale), we assessed whether the relative importance of environmental and spatial factors shaping metacommunity structure varies predictably across spatial scales, and tested how the importance of different dispersal routes vary across spatial scales. We also studied if different dispersal ability groups differ in the balance between environmental and spatial control. Variation partitioning showed that environmental factors relative to spatial factors were more important for community composition at the within‐stream scale. In contrast, spatial factors (i.e., eigenvectors from Moran's eigenvector maps) relative to environmental factors were more important at the among‐sub‐basin scale. These results indicate that environmental filtering is likely to be more important at the smallest scale with highest connectivity, while dispersal limitation seems to be more important at the largest scale with lowest connectivity. Community variation at the among‐stream and among‐sub‐basin scales were strongly explained by geographical and topographical distances, indicating that overland pathways might be the main dispersal route at the larger scales among more isolated sites. The relative effect of environmental and spatial factors on insect communities varied between low and high dispersal ability groups; this variation was inconsistent among three hierarchical scales. In sum, our study indicates that spatial scale, connectivity, and dispersal ability jointly shape stream metacommunities. [ABSTRACT FROM AUTHOR]

Aim: The factors driving microbial community β‐diversity (variation in composition) at different spatial scales yield fundamental insights into the mechanisms that maintain ecosystem biodiversity, which as yet are uncertain. Here, we explore whether spatial scale‐dependent patterns of β‐diversity vary between microbial functional groups and bacterial taxa (i.e., diazotrophic and bacterial communities) across local to regional scales (from metres to hundreds of kilometres). Location: Eastern China. Time period: October and November 2015. Major taxa studied: Diazotrophic and bacterial communities. Methods: We use two complementary statistical tools to unveil biotic mechanisms (i.e., species association) underlying variation in β‐diversity of diazotrophic and bacterial communities. We examined distance–decay slopes of both communities at the local (1–113 m), meso‐ (3.4–39 km) and regional (103–668 km) scales. We used an environmentally constrained checkerboard score and topological features of association networks as indices of species association. We then calculated contributions of species association, abiotic factors and geographical distance to explain community β‐diversity. The scale‐dependent distance–decay relationships were also examined in ubiquitous (high occupancy across samples) and endemic communities of diazotrophs and bacteria. Results: Diazotrophs displayed steeper distance–decay slopes than bacteria, suggesting that the β‐diversity of diazotrophic communities was more variable. The distance–decay slopes were dependent on spatial scales in both communities, owing to different contributions of geographical distance, abiotic factors and species association at three spatial scales. Intriguingly, species association was greater and contributed more to community β‐diversity than other forces at the local scale, implying that species association could greatly alter community structures. Main conclusions: Drivers of diazotrophic and bacterial community β‐diversity depended on spatial scales, resulting in different distance–decay patterns. Moreover, this was the first study to use two methods to demonstrate that species association played important, but as yet unrecognized, roles in driving spatial scale‐dependent β‐diversity. [ABSTRACT FROM AUTHOR]

ABSTRACT Aim While ecologists have long been interested in diversity in mountain regions, elevational patterns in beta diversity are still rarely studied across different life forms ranging from micro- to macroorganisms. Also, it is not known whether the patterns in turnover among organism groups are affected by the degree to which the environment is modified by human activities. Location Laojun Mountain, Yunnan Province, China. Methods The beta diversity patterns of benthic microorganisms (i.e. diatoms and bacteria) and macroorganisms (i.e. macroinvertebrates) in a stony stream were simultaneously investigated between elevations of 1820 and 4050 m. Data were analysed by using a distance-based approach and variation partitioning based on canonical redundancy analysis. Results Analyses of community dissimilarities between adjacent sampling sites showed comparable small-scale beta diversity along the elevational gradient for the organism groups. However, bacteria clearly showed the lowest elevational turnover when analyses were conducted simultaneously for all pairwise sites. Variation partitioning indicated that species turnover was mostly related to environmental heterogeneity and spatial gradients including horizontal distance and elevation, while purely human impacts were shown to be less important. Main conclusions The elevational beta diversity at large scales was lower for bacteria than for eukaryotic microorganisms or macroorganisms, perhaps indicative of high dispersal ability and good adaptability of bacteria to harsh environmental conditions. However, the small-scale beta diversity did not differ among the groups. Elevation was the major driver for the turnover of eukaryotic organisms, while the turnover of bacteria was correlated more with environmental variation. [ABSTRACT FROM AUTHOR]

Summary Although phylogenetic approaches are useful for providing insights into the processes underlying biodiversity patterns, the studies of microbial phylogenetic relatedness are rare, especially for elevational gradients. Using high-throughput pyrosequencing, we examined the biodiversity patterns for biofilm bacterial communities that were scraped from stream stones along an elevational gradient from 1820 to 4050 m in China. The patterns of bacterial species richness and phylogenetic diversity were hollow towards higher elevations. The bacterial communities consisted of closer relatives than expected and displayed increasing terminal phylogenetic clustering towards mountain top. The increasing phylogenetic clustering with elevation contrasts reports for macroorganisms that revealed phylogenetic overdispersion at low or intermediate elevations. Because water temperature showed the strongest correlation with phylogenetic relatedness ( r2 = 0.516), the elevational pattern in the bacterial phylogenetic structure indicated that environmental filtering possibly due to lower temperature or more frequent temperature fluctuations increased towards higher elevations. Evidence supporting the environmental filtering on bacteria was also reflected by the orderly succession in the relative abundance of different bacterial phyla along the elevational gradient and in the high evenness of bacterial taxa at higher elevations. Overall, our results indicated that ecological processes possibly related to temperature may play a dominant role in structuring bacterial biodiversity along the elevational gradient. [ABSTRACT FROM AUTHOR]

Data and analyses of elevational gradients in diversity have been central to the development and evaluation of a range of general theories of biodiversity. Elevational diversity patterns have, however, been severely understudied for microbes, which often represent decomposer subsystems. Consequently, generalities in the patterns of elevational diversity across different trophic levels remain poorly understood. Our aim was to examine elevational gradients in the diversity of macroinvertebrates, diatoms and bacteria along a stony stream that covered a large elevational gradient. Laojun Mountain, Yunnan province, China. The sampling scheme included 26 sites spaced at elevational intervals of 89 m from 1820 to 4050 m elevation along a stony stream. Macroinvertebrate and diatom richness were determined based on the morphology of the specimens. Taxonomic richness for bacteria was quantified using a molecular fingerprinting method. Over 50 environmental variables were measured at each site to quantify environmental variables that could correlate with the patterns of diversity. We used eigenvector-based spatial filters with multiple regressions to account for spatial autocorrelation. The bacterial richness followed an unexpected monotonic increase with elevation. Diatoms decreased monotonically, and macroinvertebrate richness showed a clear unimodal pattern with elevation. The unimodal richness pattern for macroinvertebrates was best explained by the mid-domain effect ( r = 0.72). The diatom richness was best explained by the variation in nutrient supply, and the increase in bacterial richness with elevation may be related to an increased carbon supply. We found contrasting patterns in elevational diversity among the three studied multi-trophic groups comprising unicellular and multicellular aquatic taxa. We also found that there may be fundamental differences in the mechanisms underlying these species diversity patterns. [ABSTRACT FROM AUTHOR]

• Cyanobacterial communities were investigated in 59 waterbodies of China. • Taxonomic diversity increased but phylogenetic diversity decreased along trophic state. • Niche width and overlap decreased from low- to high-nutrient waterbodies. • Ecological uniqueness tended to increase in more eutrophic waterbodies. • Cyanobacterial community became more similar in more eutrophic waterbodies. Eutrophication of inland waters is a mostly anthropogenic phenomenon impacting aquatic biodiversity worldwide, and might change biotic community structure and ecosystem functions. However, little is known about the patterns of cyanobacterial community variations and changes both on alpha and beta diversity levels in response to eutrophication. Here, we investigated cyanobacterial communities sampled at 140 sites from 59 lakes and reservoirs along a strong eutrophication gradient in eastern China through using CPC -IGS and 16S rRNA gene amplicon sequencing. We found that taxonomic diversity increased, but phylogenetic diversity decreased significantly along the eutrophication gradient. Both niche width and niche overlap of cyanobacteria significantly decreased from low- to high-nutrient waterbodies. Cyanobacterial community distance-decay relationship became weaker from mesotrophic to hypereutrophic waterbodies, while ecological uniqueness (i.e., local contributions to beta diversity) tended to increase in high-nutrient waterbodies. Latitude and longitude were more important in shaping cyanobacterial community structure than other environmental variables. These findings suggest that eutrophication affects alpha and beta diversity of cyanobacterial communities, leading to increasingly similar community structures in lakes and reservoirs with a higher level of eutrophication. Our work highlights how cyanobacterial communities respond to anthropogenic eutrophication and calls for an urgent need to develop conservation and management strategies to control lake eutrophication and protect freshwater biodiversity. [Display omitted] [ABSTRACT FROM AUTHOR]

Background: Understanding the large-scale patterns of microbial functional diversity is essential for anticipating climate change impacts on ecosystems worldwide. However, studies of functional biogeography remain scarce for microorganisms, especially in freshwater ecosystems. Here we study 15,289 functional genes of stream biofilm microbes along three elevational gradients in Norway, Spain and China., Results: We find that alpha diversity declines towards high elevations and assemblage composition shows increasing turnover with greater elevational distances. These elevational patterns are highly consistent across mountains, kingdoms and functional categories and exhibit the strongest trends in China due to its largest environmental gradients. Across mountains, functional gene assemblages differ in alpha diversity and composition between the mountains in Europe and Asia. Climate, such as mean temperature of the warmest quarter or mean precipitation of the coldest quarter, is the best predictor of alpha diversity and assemblage composition at both mountain and continental scales, with local non-climatic predictors gaining more importance at mountain scale. Under future climate, we project substantial variations in alpha diversity and assemblage composition across the Eurasian river network, primarily occurring in northern and central regions, respectively., Conclusions: We conclude that climate controls microbial functional gene diversity in streams at large spatial scales; therefore, the underlying ecosystem processes are highly sensitive to climate variations, especially at high latitudes. This biogeographical framework for microbial functional diversity serves as a baseline to anticipate ecosystem responses and biogeochemical feedback to ongoing climate change. Video Abstract.