Effects Of Climate And Human Activities On Microbial Communities In Typical Freshwater Bodies

According to extensive global climate change and human activities,freshwater ecosystems are greatly affected.As an important part of freshwater bodies,microorganisms are sensitive to environmental changes and are important water quality indicators.Given that microbes play a critical role on biogeochemical cycles,and drive essential ecosystem services,increasing knowledge of biodiversity patterns and their underlying mechanisms is therefore vital for an integrated understanding and protection of water environment.Here,we chose Tibetan Plateau streams and Mochou Lake as our study sites.The Tibetan Plateau is the largest and highest plateau in the world,which has unique ecological environment.We examined stream bacterial and fungal communities along an elevational gradient of 990–4,600 m with a geographic distance up to 500 km in Tibetan Plateau and further analyzed their elevational patterns and drivers of species richness,ecological uniqueness,community composition and microbial network.Mochou Lake is a typical urban lake,which is usually under a condition of eutrophication in summer and autumn.A 10-month ecological enclosure experiment was carried out in Mochou Lake.A total of 24 mesocosms were set up,and 6treatment groups were set up with 4 parallels,including control mesocosms,mesocosms with and without nutrients amendment,mesocosms with and without aquatic plants,and mesocosms with and without aquatic plants harvest.In Tibetan Plateau,bacteria and fungi showed distinct elevational trends in species richness and consistently decreasing patterns in their ecological uniqueness.The distance-decay relationships were concordant for the two microbial groups,while fungi showed higher dissimilarity and a lower turnover rate.Interestingly,bacterial and fungal compositions substantially differed between the elevations below and above 3,000 m.Co-occurrence network analysis showed that bacteria have higher complexity and aggregation than fungi.While fungi had higher niche constraints in the same habitat,and its complexity was positively correlated with elevation.Climate predictors,such as the mean annual temperature and precipitation seasonality,had greater effects than local environment drivers.Notably,fungal diversity was mainly influenced by climate,while bacterial diversity was explained by the shared contributions of climate and local factors.In the mesocosm experiment of Mochou Lake,the mesocosm water was in a state of eutrophication.The microbial diversity index had obvious seasonal changes.The main phyla were Proteobacteria,Actinobacteria,and Bacteroidetes,and the sum of the relative abundances accounted for up to 80% of the whole community.The comparison among the different mesocosms showed that in July and August,the addition of nutrients reduced the species richness and the Pielou index of microorganisms.Planting aquatic plants could increase microbial diversity,indicating that aquatic plants offset the weakening effect of nitrogen addition on water microbes.Water temperature was the main driving factor of bacterial species diversity and evenness,and transparency was the main influencing factor of community uniqueness.In conclusion,this study revealed the temporal and spatial variation patterns of water microbial communities,and the response mechanisms of microbial communities to environmental changes,such as climate,physicochemical factors,and aquatic plants.The study emphasized the role of climate and human factors on microbial communities,and provided basic data for understanding the insights of microbial changes and improving environment management.