Environmental and spatial contributions to tree community assembly across life stages and scales in evergreen-deciduous broadleaf karst forests,southwest China

Spatial and environmental processes are two ecological processes that have attracted considerable attention in plant community assembly,depending on sampling scale and life history.However,the processes that determine community assembly have not been studied in the karst region of southwest China.In this study,a 25-ha(500 m×500 m)monitoring plot within the subtropical climax forest in the karst region was established and canonical correspondence analysis was used to reveal the effects of topography and soil on the spatial patterns of tree community assembly.Our study suggests that spatial processes dominate species composition and the combined effects of spatial and environmental processes play an important role.Overall interpretation rate increases with enlarging the sampling scale.However,the pattern of variation partitioning was similar in different life stages.Environmental variables significantly affected species composition at different sampling sizes and life histories and had a higher interpretation rate of species composition on larger s ampling sizes.Topographic wetness index was the most important variable to explain species composition of the environmental variables.These results suggest that it is necessary to consider the relative importance of environmental and spatial factors on community assembly to better understand,conserve,and manage subtropical karst forests.

Adaptive genetic diversity of dominant species contributes to species co-existence and community assembly

The synthesis of evolutionary biology and community ecology aims to understand how genetic variation within one species can shape community properties and how the ecological properties of a community can drive the evolution of a species.A rarely explored aspect is whether the interaction of genetic variation and community properties depends on the species'ecological role.Here we investigated the interactions among environmental factors,species diversity,and the within-species genetic diversity of species with different ecological roles.Using high-throughput DNA sequencing,we genotyped a canopydominant tree species,Parashorea chinensis,and an understory-abundant species,Pittosporopsis kerrii,from fifteen plots in Xishuangbanna tropical seasonal rainforest and estimated their adaptive,neutral and total genetic diversity;we also surveyed species diversity and assayed key soil nutrients.Structural equation modelling revealed that soil nitrogen availability created an opposing effect in species diversity and adaptive genetic diversity of the canopy-dominant Pa.chinensis.The increased adaptive genetic diversity of Pa.chinensis led to greater species diversity by promoting co-existence.Increased species diversity reduced the adaptive genetic diversity of the dominant understory species,Pi.kerrii,which was promoted by the adaptive genetic diversity of the canopy-dominant Pa.chinensis.However,such relationships were absent when neutral genetic diversity or total genetic diversity were used in the model.Our results demonstrated the important ecological interaction between adaptive genetic diversity and species diversity,but the pattern of the interaction depends on the identity of the species.Our results highlight the significant ecological role of dominant species in competitive interactions and regulation of community structure.

Ontogenetic trait variation and metacommunity effects influence species relative abundances during tree community assembly

Predicting species abundance is one of the most fundamental pursuits of ecology.Combining the information encoded in functional traits and metacommunities provides a new perspective to predict the abundance of species in communities.We applied a community assembly via trait selection model to predict quadrat-scale species abundances using functional trait variation on ontogenetic stages and metacommunity information for over 490 plant species in a subtropical forest and a lowland tropical forest in Yunnan,China.The relative importance of trait-based selection,mass effects,and stochasticity in shaping local species abundances is evaluated using different null models.We found both mass effects and trait selection contribute to local abundance patterns.Trait selection was detectable at all studied spatial scales(0.04e1 ha),with its strength stronger at larger scales and in the subtropical forest.In contrast,the importance of stochasticity decreased with spatial scale.A significant mass effect of the metacommunity was observed at small spatial scales.Our results indicate that tree community assembly is primarily driven by ontogenetic traits and metacommunity effects.Our findings also demonstrate that including ontogenetic trait variation into predictive frameworks allows ecologists to infer ecological mechanisms operating in community assembly at the individual level.

Stochastic community assembly of abundant taxa maintains the relationship of soil biodiversity-multifunctionality under mercury stress

Soil abundant taxa diversity positively related to multifunctionality under Hg stress.•Microbial network complexity of soil abundant taxa supported the strength of SBF.•Stochastic assembly of soil abundant subcommunity supported the strength of SBF.•Stochastic ratio was the most important predictor for the strength of SBF.It is known that soil microbial communities are intricately linked to multiple ecosystem functions and can maintain the relationship between soil biodiversity and multifunctionality(SBF)under environmental stresses.However,the relative contributions and driving forces of abundant and rare taxa within the communities in maintaining soil biodiversity-multifunctionality relationship under pollution stresses are still unclear.Here,we conducted microcosm experiments to estimate the importance of soil abundant and rare taxa in predicting these relationships under heavy metal mercury(Hg)stress in paired paddy and upland fields.The results revealed that the diversity of abundant taxa,rather than rare taxa,was positively related to multifunctionality,with the abundant subcommunity tending to maintain a larger proportion of soil functions including chitin degradation,protein degradation,and phosphorus mineralization.Soil multitrophic network complexity consisting of abundant species showed positive correlations with biodiversity and multifunctionality,and supported the strength of SBF within a network complexity range.Stochastic assembly processes of the abundant subcommunity were positively correlated with the strength of SBF,although stochastic processes decreased the biodiversity and the multifunctionality,respectively.After simultaneously accounting for multiple factors on the strength of SBF,we found that the stochastic community assembly ratio of abundant taxa was the most important predictor for SBF strength under Hg stress.Our results highlight the importance of abundant taxa in supporting soil multifunctionality,and elucidate the linkages between community assembly,network complexity and SBF relationship under environmental stresses.

Response and assembly of abundant and rare taxa in Zaopei under different combination patterns of Daqu and pit mud:from microbial ecology to Baijiu brewing microecosystem

The quality and aroma of strong-flavor Baijiu are mainly dependent on Daqu,pit mud(PM),and the interaction of both.However,little is known about how their combination patterns affect the microbiome and metabolome of Zaopei,especially the metabolic function of rare taxa.Here,an experiment on industrial size was designed to assess the effects of 6 combinations(3 kinds of Daqu×2 kinds of PM)on the composition and assembly of different taxa,as well as the flavor profile.The results showed that Zaopei's microbiota was composed of a few abundant taxa and enormous rare taxa,and rare bacterial and abundant fungal subcommunities were significantly affected by combination patterns.The assembly processes of abundant/rare taxa and bacterial/fungal communities were distinct,and environmental changes mediated the balance between stochastic and deterministic processes in rare bacteria assembly.Furthermore,specific combination patterns improved the flavor quality of Zaopei by enhancing the interspecies interaction,which was closely related to rare taxa,especially rare bacteria.These findings highlighted that rare bacteria might be the keystone in involving community interaction and maintaining metabolic function,which provided a scientific foundation for better understanding and regulating the brewing microbiota from the viewpoint of microbial ecology.

Does disturbance regime change community assembly of angiosperm plant communities in the boreal forest?

Aims To examine if and how species and phylogenetic diversity change in relation to disturbance,we conducted a review of ecological literature by testing the consistency of the relationship between phylogenetic diversity and disturbance and compared taxonomic groups,type of disturbance and ecosystem/habitat context.We provide a case study of the phylogenetic diversity–disturbance relationship in angiosperm plant communities of a boreal forest region,compared with types of natural and anthropogenic disturbances and plant growth forms.Methods Using a large-scale sampling plot network along a complete(0–100%)anthropogenic disturbance gradient in the boreal biome,we compared the changes of angiosperm plant community structure and composition across plots.We estimated natural disturbance with historical records of major fires.We then calculated phylogenetic diversity indexes and determined species richness in order to compare linear and polynomial trends along disturbance gradients.We also compared the changes of community structure for different types of anthropogenic disturbances and examined how the relationships between species and phylogenetic diversity and disturbance regimes vary among three different life forms(i.e.forbs,graminoids and woody plants).Important Findings Phylogenetic diversity was inconsistently related to disturbance in previous studies,regardless of taxon,disturbance type or ecosystem context.In the understudied boreal ecosystem,angiosperm plant communities varied greatly in species richness and phylogenetic diversity along anthropogenic disturbance gradients and among different disturbance types.In general,a quadratic curve described the relationship between species richness and anthropogenic disturbance,with the highest richness at intermediate anthropogenic disturbance levels.However,phylogenetic diversity was not related to disturbance in any consistent manner and species richness was not correlated with phylogenetic diversity.Phylogenetic relatedness was also inconsistent across plant growth forms and different anthropogenic disturbance types.Unlike the inconsistent patterns observed for anthropogenic disturbance,community assembly among localities varying in time since natural disturbance exhibited a distinct signature of phylogenetic relatedness,although those trends varied among plant growth forms.

Experimental evidence that soil heterogeneity enhances plant diversity during community assembly

Aims Environmental heterogeneity is a primary mechanism explain-ing species coexistence and extant patterns of diversity.Despite strong theoretical support and ample observational evidence,few experimental studies in plant communities have been able to demonstrate a causal link between environmental heterogene-ity and plant diversity.This lack of experimental evidence sug-gests that either fine-scale heterogeneity has weak effects on plant diversity or previous experiments have been unable to effectively manipulate heterogeneity.Here,we utilize a unique soil manipu-lation to test whether fine-scale soil heterogeneity will increase plant richness through species sorting among experimental patch types.Methods This experiment was conducted in the tallgrass prairie region of south-central Kansas,USA.We utilized the inherent variation found in the vertical soil profile,which varied in both biotic and abiotic characteristics,and redistributed these strata into either homoge-neous or heterogeneous spatial arrangements in 2.4×2.4 m plots.After the soil manipulation,34 native prairie species were sown into all plots.We conducted annual censuses at peak biomass to quantify species composition and plant density by species within the experimental communities.Important Findings After 2 years,species richness was significantly higher in heteroge-neous relative to homogeneous plots and this pattern was independ-ent of total plant density.In the heterogeneous plots,13 species had higher establishment in a specific patch type representing one of the three soil strata.Conversely,no species had greater estab-lishment in the mixed stratum,which comprised the homogene-ous plots,relative to the heterogeneous strata.These species sorting patterns suggest that fine-scale heterogeneity creates opportunities for plant establishment due to niche differences,which translates into increased plant diversity at the plot scale.Species richness was more strongly related to plant density among patches comprising homogenous plots-where fine-scale heterogeneity was minimized,but weak in heterogeneous plots.This pattern is consistent with the idea that richness-density relationships dominate when neutral pro-cesses are important but are weak when niche processes operate.Unlike many previous attempts,our results provide clear,experi-mental evidence that fine-scale soil heterogeneity increases species richness through species sorting during community assembly.

Community structure and assembly of denitrifying bacteria in epiphytic biofilms in a freshwater lake ecosystem

Denitrifying bacteria are a crucial component of aquatic ecosystem in nitrogen cycle.However,the denitrifying bacterial community dynamics and structure in epiphytic biofilms remain unexplored.The abundance of denitrification gene(nir)and structure of nirS-denitrifying bacterial community in the epiphytic biofilms collected in July and November of 2018 from a typical plateau lake(Caohai Wetland,Guizhou,China)were studied by Real-time Quantitative Polymerase Chain Reaction(qPCR)and highthroughput sequencing.Results show that the gene abundance of nirK was higher than that of nirS(P<0.05),and it was significantly different during the growth period(July)than the decline period(November).The denitrifying bacterial species was similar in the two months and shared 76.18%of OTUs.Proteobacteria(56.55%±22.15%)was the dominant phylum in all the samples.Epiphytic biofilms between growth period and decline period displayed significantly different microbial community structures due to differences in species abundance.Water temperature was the crucial factor that affected the denitrifying microbial community structure in our study.Environmental factors explain only partially the dynamic characteristics of denitrifying microbial communities,implying that the stochastic processes affected the construction of denitrifying microbial communities.As the null model analysis results show,dispersal limitation(stochastic)and undominated processes significantly influenced the assembly of denitrifying microbial communities.This study broadened our understanding of the denitrifying bacterial community structure and its function on epiphytic biofilms in freshwater ecosystems with new information provided.

Intraspecific trait variation improves the detection of deterministic community assembly processes in early successional forests,but not in late successional forests

Aims Intraspecific trait variation(ITV)has been increasingly recognized to play an important role in understanding the underlying processes influencing community assembly.However,gaps remain in our understanding of how incorporating ITV will influence the relative importance of deterministic(e.g.habitat filtering,limiting similarity)and stochastic processes in driving community assembly at different successional stages.Methods We used data for eight functional traits from 55 woody species in early(24 ha)and late(25 ha)successional temperate forest plot in northeast China.We employed an approximate Bayesian com-putation approach to assess the relative contribution of stochastic processes,habitat filtering and limiting similarity in driving commu-nity structure.We then compared the results with and without intra-specific trait variation to investigate how ITV influences the inferred importance of each process.Important Findings We found that when analyzing interspecific trait variation only(i.e.without ITV),stochastic processes were observed most frequently in driving community composition,followed by habitat filtering and limiting similarity in both forests.However,ITV analyses showed that the relative importance of both deterministic processes(habitat filtering and limiting similarity)increased in early successional for-est,but remained virtually unchanged in late successional forest.Our study reveals the distinctive influence of ITV on the inference of underlying processes in a context of succession and reinforces the need to estimate ITV for making correct inferences about underlying ecological processes.

Green manuring facilitates bacterial community dispersal across different compartments of subsequent tobacco

Green manure–crop rotation is a sustainable approach to protect crops against diseases and improve yield.However,the mechanism by which green manuring manipulates the crop-associated microbial community remains to be elucidated.In this study,we explored the horizontal processes of bacterial communities in different compartments of the soil–root interface(bulk soil,rhizosphere soil,rhizoplane and endosphere)of tobacco by performing a field experiment including four rotation practices,namely,tobacco rotated with smooth vetch,ryegrass,radish,and winter fallow(without green manure).Results showed that the co-occurrence networks constructed by adjacent compartments of the soil–root interface with green manuring had more edges than without green manuring,indicating dramatic microbial interactions.Green manuring increased the dispersal-niche continuum index between bulk soil and other compartments,indicating that it facilitated the horizontal dispersal of microbes.For the different green manuring practices,the neutral community model explained 24.6–27.6%of detection frequency for bacteria,and at least one compartment under each practice had a normalized stochasticity ratio higher than the 50%boundary point,suggesting that the deterministic and stochastic processes jointly shaped the tobacco microbiome.In conclusion,green manuring generally facilitates bacterial community dispersal across different compartments and enhances potential interactions among adjacent compartments.This study provides empirical evidence for understanding the microbiome assembly under green manure–crop rotation.

Mixing regime shapes the community assembly process,microbial interaction and proliferation of cyanobacterial species Planktothrix in a stratified lake

Lake mixing influences aquatic chemical properties and microbial community composition,and thus,we hypothesized that it would alter microbial community assembly and interac-tion.To clarify this issue,we explored the community assembly processes and cooccurrence networks in four seasons at two depths(epilimnion and hypolimnion)in a mesotrophic and stratified lake(Chenghai Lake),which formed stratification in the summer and turnover in the winter.During the stratification period,the epilimnion and hypolimnion went through contrary assembly processes but converged to similar assembly patterns in the mixing pe-riod.In a highly homogeneous selection environment,species with low niche breadth were filtered,resulting in decreased species richness.Water mixing in the winter homogenized the environment,resulting in a simpler microbial cooccurrence network.Interestingly,we observed a high abundance of the cyanobacterial genus Planktothrix in the winter,proba-bly due to nutrient redistribution and Planktothrix adaptivity to the winter environment in which mixing played important roles.Our study provides deeper fundamental insights into how environmental factors influence microbial community structure through community assembly processes.

Distinct community assembly processes underlie significant spatiotemporal dynamics of abundant and rare bacterioplankton in the Yangtze River

The rare microbial biosphere provides broad ecological services and resilience to various ecosystems.Nevertheless,the biogeographical patterns and assembly processes of rare bacterioplankton communities in large rivers remain uncertain.In this study,we investigated the biogeography and community assembly processes of abundant and rare bacterioplankton taxa in the Yangtze River(China)covering a distance of 4300 km.The results revealed similar spatiotemporal patterns of abundant taxa(AT)and rare taxa(RT)at both taxonomic and phylogenetic levels,and analysis of similarities revealed that RT was significantly influenced by season and landform than AT.Furthermore,RT correlated with more environmental factors than AT,whereas environmental and spatial factors explained a lower proportion of community shifts in RT than in AT.The steeper distance–decay slopes in AT indicated higher spatial turnover rates of abundant subcommunities than rare subcommunities.The null model revealed that both AT and RT were mainly governed by stochastic processes.However,dispersal limitation primarily governed the AT,whereas the undominated process accounted for a higher fraction of stochastic processes in RT.River flow and suspended solids mediated the balance between the stochastic and deterministic processes in RT.The spatiotemporal dynamics and assembly processes of total taxa were more similar as AT than RT.This study provides new insights into both significant spatiotemporal dynamics and inconsistent assembly processes of AT and RT in large rivers.

Unravelling how biochar and dung amendments determine the functional structure and community assembly related to methane metabolisms in grassland soils

Biochar and dung amendments have been extensively employed in soil remediation and fertilization of grasslands,which are the largest terrestrial sinks for methane.However,how these exogenous amendments regulate methane metabolisms at the molecular and community levels remains elusive.In this study,we investigated the functional genes and community assemblies of methanogens and methanotrophs using Geochip 5.0 and high-throughput sequencing to reveal the impacts of biochar and dung on soil methanogenesis and methane oxidation.The interac-tions between methane metabolic genes and other biogeochemical genes were also examined.According to Geo-chip microarrays,methanogenic gene mcrA decreased and increased with dung or biochar amendment,respectively;The methanotrophic gene pmoA showed a reverse but not significant tendency.Undominated processes contributed 65.51%to replace homogeneous selections as primary driving forces of methanogen assembly after dung amend-ment;the contribution of dispersal limitation increased to 46.13%in methanotroph assembly after biochar amend-ment.The diversity and association of co-occurrence networks for carbon-nitrogen cycling genes decreased after exogenous amendments.These results indicated that biochar and dung amendments prominently regulated the functional genes and community assembly involved in methane metabolisms.The co-existence patterns of methane metabolic genes and other related geochemical genes were also shaped by these amendments.This study provides the scientific reference for the development of grassland management in the context of global warming.

Temporal characteristics of algae-denitrifying bacteria co-occurrence patterns and denitrifier assembly in epiphytic biofilms on submerged macrophytes in Caohai Lake,SW China

Denitrifying bacteria in epiphytic biofilms play a crucial role in nitrogen cycle in aquatic habitats.However,little is known about the connection between algae and denitrifying bacteria and their assembly processes in epiphytic biofilms.Epiphytic biofilms were collected from submerged macrophytes(Patamogeton lucens and Najas marina L.)in the Caohai Lake,Guizhou,SW China,from July to November 2020 to:(1)investigate the impact of abiotic and biotic variables on denitrifying bacterial communities;(2)investigate the temporal variation of the algae-denitrifying bacteria co-occurrence networks;and(3)determine the contribution of deterministic and stochastic processes to the formation of denitrifying bacterial communities.Abiotic and biotic factors influenced the variation in the denitrifying bacterial community,as shown in the Mantel test.The co-occurrence network analysis unveiled intricate interactions among algae to denitrifying bacteria.Denitrifying bacterial community co-occurrence network complexity(larger average degrees representing stronger network complexity)increased continuously from July to September and decreased in October before increasing in November.The co-occurrence network complexity of the algae and nirS-encoding denitrifying bacteria tended to increase from July to November.The co-occurrence network complexity of the algal and denitrifying bacterial communities was modified by ammonia nitrogen(NH_(4)^(+)-N)and total phosphorus(TP),pH,and water temperature(WT),according to the ordinary least-squares(OLS)model.The modified stochasticity ratio(MST)results reveal that deterministic selection dominated the assembly of denitrifying bacterial communities.The influence of environmental variables to denitrifying bacterial communities,as well as characteristics of algal-bacterial co-occurrence networks and the assembly process of denitrifying bacterial communities,were discovered in epiphytic biofilms in this study.The findings could aid in the appropriate understanding and use of epiphytic biofilms denitrification function,as well as the enhancement of water quality.

Deterministic processes drive turnover-dominated beta diversity of breeding birds along the central Himalayan elevation gradient

Beta diversity,the variation of community composition among sites,bridges alpha and gamma diversity and can reveal the mechanisms of community assembly through applying distance-decay models and/or partitioning beta diversity into turnover and nestedness components from functional and phylogenetic perspectives.Mountains as the most natural experiment system provide good opportunities for exploring beta diversity patterns and the underlying ecological processes.Here,we simultaneously consider distance-decay models and multiple di-mensions of beta diversity to examine spatial variations of bird communities,and to evaluate the relative importance of niche-based and neutral community assembly mechanisms along a 3600-m elevational gradient in the central Himalayas,China.Our results showed that species turnover dominates taxonomic,functional,and phylogenetic beta diversity.We observed strongest evidence of spatial distance decays in taxonomic similarities of birds,followed by its phylogenetic and functional analogues.Turnover component was highest in taxonomic beta diversity,while nestedness component was highest in functional beta diversity.Further,all correlations of assemblage similarity with climatic distance were higher than that with spatial distances.Standardized values of overall taxonomic,functional,and phylogenetic beta diversity and their turnover components increase with increasing elevational distance,while the standardized values of taxonomic and phylogenetic nestedness decreased with increasing elevational distance.Our results highlighted the niche-based deterministic processes in shaping elevational bird diversity patterns that were determined by the relative roles of decreasing trend of environmental filtering and increasing trend of limiting similarity along elevation distances.

TIL20: A review of island biogeography and habitat fragmentation studies on subtropical reservoir islands of Thousand Island Lake, China

Reservoir islands formed by dam construction have the same history,clear boundaries,and large numbers that provide a natural platform for testing theories in ecology and biogeography.In this paper,we review studies of multiple zoological taxa on reservoir islands of a large lake in eastern China(Thousand Island Lake).This lake,created in 1959,has 1078 artificial land-bridge islands of varying areas and isolation.Our review summarizes the decades-long studies in island biogeography and habitat fragmentation from this island system,grouped into three topics:species richness(“how many species are there”),community structure(“who are they”),and species interaction(“how they interact with each other”).Our findings support the predictions of the Equilibrium Theory of Island Biogeography and extend this theory to predict community structure of island faunas by moving beyond assumptions of species equivalency.In addition,the extensive studies on ecological networks,including mutualistic,antagonistic,and parasitic interactions,reveal the negative impacts of habitat loss on the maintenance of such networks,even as increasing forest edge enhances the robustness of pollination networks.At the end of this review,we proposed several future research directions based on current studies that are simultaneously at the frontier of ecology and biogeography.

Assembly and co-occurrence patterns of rare and abundant bacterial sub-communities in rice rhizosphere soil under short-term nitrogen deep placement

Nitrogen(N)deep placement has been found to reduce N leaching and increase N use efficiency in paddy fields.However,relatively little is known how bacterial consortia,especially abundant and rare taxa,respond to N deep placement,which is critical for understanding the biodiversity and function of agricultural ecosystem.In this study,lllumina sequencing and ecological models were conducted to examine the diversity patterns and underlying assembly mechanisms of abundant and rare taxa in rice rhizosphere soil under different N fertilization regimes at four rice growth stages in paddy fields.The results showed that abundant and rare bacteria had distinct distribution patterns in rhizosphere samples.Abundant bacteria showed ubiquitous distribution;while rare taxa exhibited uneven distribution across all samples.Stochastic processes dominated community assembly of both abundant and rare bacteria,with dispersal limitation playing a more vital role in abundant bacteria,and undominated processes playing a more important role in rare bacteria.The N deep placement was associated with a greater influence of dispersal limitation than the broadcast N fertilizer(BN)and no N fertilizer(NN)treatments in abundant and rare taxa of rhizosphere soil;while greater contributions from homogenizing dispersal were observed for BN and NN in rare taxa.Network analysis indicated that abundant taxa with closer relationships were usually more likely to occupy the central position of the network than rare taxa.Nevertheless,most of the keystone species were rare taxa and might have played essential roles in maintaining the network stability.Overall,these findings highlighted that the ecological mechanisms and co-occurrence patterns of abundant and rare bacteria in rhizosphere soil under N deep placement.

Novel evidence from Taxus fuana forests for niche-neutral process assembling community

Background:Understanding the mechanisms underlying community assembly is helpful for conservation and restoration of communities, particularly those that contain rare and endangered species like Taxus fuana, which are endemic to the Western Himalayas. The niche (limiting similarity) vs. neutral (randomness) assembly of the T.fuana forest community in Gyirong County, Tibet, China, was investigated. The net relatedness index (NRI) was calculated using a phylogenetic tree. The phylogenetic characteristics of the community and its relationships with environment were analyzed.Results:The value of the mean NRI at the community level was less than-1.96, indicating that the phylogenetic structure was overdispersed;whereas majority of the NRIs at the tree, shrub, and herb layers were within-1.96 to1.96, indicating random dispersion. Environmental factors accounted for 44.38%, 46.52%, 24.04%, and 14.07%of the variation at the community level, tree, shrub, and herb layer, respectively. The phylogenetic structure at the community level and tree layer were significantly influenced by both topographic and soil factors, while shrub and herb layers tended to be affected by a single environmental factor.Conclusions:Community assembly of the T. fuana forest was simultaneously affected by niche and neutral processes, and their variations were closely related to the environment. Neutral process dominated community assembly in the shrub and herb layers. However, the interaction of limiting similarity and randomness played a dominant role at the community level and tree layer;and contributed to maintenance of biodiversity stability. The synergy of multiple environmental factors had a more obvious influence on community assembly than individual environmental factors, especially at the community level. These findings would help to understand the conservation of rare and endangered tree species, such as T. fuana, in the native community;and highlight the importance of random and non-random processes in assembly and biodiversity maintenance of alpine plant communities.

Changes in diversity,composition and assembly processes of soil microbial communities during Robinia pseudoacacia L.restoration on the Loess Plateau,China

Robinia pseudoacacia L.(RP)restoration has increased vegetation cover in semi-arid regions on the Loess Plateau of China,but ecological problems have also occurred due to RP restoration,such as reduced soil moisture.Further,it is still uncertain how microbial diversity,composition and assembly processes change with RP restoration in semi-arid regions.Therefore,amplicon sequencing of small subunit ribosomal ribonucleic acid(16S rRNA)and internal transcribed spacer(ITS)genes was performed to study soil bacterial and fungal diversity,composition and assembly processes at four study sites with different stand ages of RP plantations(Y10,RP plantation with stand ages less than 10 a;Y15,RP plantation with stand ages approximately 15 a;Y25,RP plantation with stand ages approximately 25 a;and Y40,RP plantation with stand ages approximately 40 a)along a 40-a chronosequence on the Loess Plateau.The diversity of soil bacteria and fungi increased significantly during the restoration period from 10 to 15 a(P<0.05).However,compared with Y15,bacterial diversity was lower at Y25 and Y40,and fungal diversity remained stable during the restoration period between 25 and 40 a.The relative abundances of Proteobacteria and Ascomycota increased during the restoration period from 10 to 15 a.Conversely,after 15 a of restoration,they both decreased,whereas the relative abundances of Actinomycetes,Acidobacteria and Basidiomycota gradually increased.The variations in soil bacterial communities were mainly related to changes in soil total nitrogen,nitrate nitrogen and moisture contents,while soil fungal communities were mainly shaped by soil organic carbon and nitrate nitrogen contents.Bacterial communities were structured by the heterogeneous selection and stochastic process,while fungal communities were structured primarily by the stochastic process.The RP restoration induced an increase in the relative importance of heterogeneous selection on bacterial communities.Overall,this study reveals the changes in microbial diversity,community composition and assembly processes with RP restoration on the Loess Plateau and provides a new perspective on the effects of vegetation restoration on soil microbial communities in semi-arid regions.

Patterns of phylogenetic relatedness of non-native plants across the introduction-naturalization-invasion continuum in China

Human activities have caused the exchange of species among different parts of the world.When introduced species become naturalized and invasive,they may cause great negative impacts on the environment and human societies,and pose significant threats to biodiversity and ecosystem structure.Knowledge on phylogenetic relatedness between native and non-native species and among non-native species at different stages of species invasion may help for better understanding the drivers of species invasion.Here,I analyze a comprehensive data set including both native and non-native angiosperm species in China to determine phylogenetic relatedness of introduced species across a full invasion continuum(from introduction through naturalization to invasion).This study found that(1) introduced plants are a phylogenetically clustered subset of overall(i.e.native plus non-native) angiosperm flora,(2) naturalized plants are a phylogenetically clustered subset of introduced plants,and(3) invasive plants are a phylogenetically clustered subset of naturalized plants.These patterns hold regardless of spatial scales examined(i.e.national versus provincial scale) and whether basal-or tip-weighted metric of phylogenetic relatedness is considered.These findings are consistent with Darwin's preadaptation hypothesis.