Distribution Patterns And Assembly Mechanisms Of Microbial Communities In Tibetan Lakes

Tibetan Plateau has the largest number,the largest area,and diverse types of the alpine lakes in the world.As one of the important land landscapes of the Tibetan Plateau,lakes play an important role in the global water cycle and biogeochemical cycle,and are considered as an important indicators of global climate change and regional response.Glacial lakes are a kind of special lake formed by glacier activity,its formation and development are closely related to climate change,and it is a sensitive indicator of climate change.Microorganisms,as important drivers of the cycling of carbon,nitrogen,phosphorus,and other biological elements and energy flow in lake ecosystems,play a crucial role in maintaining the stability and ecological functions in lake ecosystems.However,our understanding about the distribution patterns and assembly mechanisms of microbial communities in Tibetan lakes is still limited,especially the spatial variation characteristics of microbial communities in glacial lakes under the global climate change.Therefore,under the background of increasingly severe climate and environmental changes,it is of great significance to systematically study the distribution patterns and assembly mechanisms of microbial communities in the Tibetan Plateau lakes for assessing and predicting the response of lake ecosystem to climate and environmental change.In this study,we used analytical chemistry,Illumina Miseq high-throughput sequencing,bioinformatics and multivariate statistical analysis to analyze the microbial sub-community distribution patterns and assembly mechanisms of Tibetan Plateau lakes from regional spatial scale to local glacial scale,and revealed the effects of glacial retreat and seasonal melting on the microbial community structure and diversity of glacial lakes.The main results and conclusions are as follows:(1)In this study,we investigated the ecological processes and co-occurrence relationships of the core and satellite bacterial sub-communities in 30 lakes on the Tibetan Plateau.Our results demonstrated that the core bacterial sub-communities exhibited similar biogeographic patterns to the satellite counterparts,but their patterns were generally shaped via different assembly mechanisms.For the core subcommunities,stochastic processes(58.19%)played important roles,while deterministic processes(62.17%)are of importance in shaping the satellite sub-community assembly.In addition,topological properties of nodes in the network demonstrated that the core sub-communities had more complex and stable co-occurrence associations.Overall,this study demonstrated the differences in the core and satellite sub-community assembly and network stability,suggesting the importance of considering species traits to understand the biogeographic distribution of bacterial communities in high-altitude lakes.(2)Based on 16 S r RNA gene and environmental data,we investigated assembly processes of the habitat generalists and specialists in sediment of Tibetan lakes and their role in the stability of metacommunity cooccurrence network.Our results showed that the habitat generalists exhibited broader environmental thresholds and closer phylogenetic clustering than specialist counterparts.In contrast,the specialists exhibited stronger phylogenetic signals of ecological preferences compared with the habitat generalists.Stochastic processes dominated the habitat generalist(63.2%)and specialist(81.3%)community assembly.Sediment p H was the major factor mediating the balance between stochastic and deterministic processes in the habitat generalists and specialists.In addition,as revealed by network analysis,the habitat specialists played a greater role in maintaining the stability of metacommunity co-occurrence network.The insights gained from this study can be helpful to understand the mechanisms underlying maintenance of sediment microbial diversity in plateau lakes.(3)By the correlation analysis of the bacterial community diversity in KQGR glacial lakes and the distance from the sampling site to the glacier,we found that bacterial diversity in lake waters decrease with increasing distance from the glacier,while diversity in sediments increases with increasing distance from the glacier.Bacterial community compositions in both habitats were significantly structured along the distance from the glacier.Bacterial communities in lake waters were primarily governed by deterministic processes,whereas those in sediments changed from stochastic to deterministic processes with increasing distance from the glacier.In addition,network analysis showed that the complexity and stability of the bacterial network were lower in distant glacial lake waters,while the complexity and stability of the bacterial network in sediments were higher.The distance between glacier and lake can measure the effect of the glacier on the lake,so these findings collectively indicated that the glacial lake water and sediment bacterial communities have different responses to glacial retreat.Our study gives a preliminary view of how lake water and sediment bacterial communities changes as consequence of the glacier retreat and provides new insights to define their past and future ecological trajectories.(4)We studied the monthly changes of bacterial community composition and diversity in glacial lakes connected to the KQGR glacier and elucidated the effect of seasonal glacial melt on t bacterial community in the glacial lake ecosystem.The results showed that bacterial diversity and community structure in both the water and sediment of KQGR glacier lakes were closely related to environmental variables.Conductivity as a main factor affecting the monthly changes of bacterial community diversity and structure in the lake water,while TN plays a key role in driving the monthly changes of bacterial community structure and diversity in glacial lake sediment.In addition,the glacial meltwater increases the role of stochastic processes in lake water,and deterministic processes are the main processes affecting the assembly of sediment bacterial communities.This study revealed the factors influencing the monthly changes of the glacial lake bacterial communities,and provided a theoretical basis for evaluating the long-term effects of glacier retreat on glacial lake ecosystems.In summary,our study elucidates the distribution patterns and assembly mechanisms of microbial sub-communities in lakes on the Tibetan Plateau,and reveals that sediment p H is the major factor regulating the assembly of sediment microbial communities in Tibetan Plateau lakes.In addition,we clarified the effects of glacial retreat and seasonal melting on the structure and diversity of microbial communities in glacial lake water and sediment from spatial and temporal scales.These studies are important for predicting the response of microbial communities in Tibetan Plateau lakes to global climate change.