A Preliminary Study On The Spatial Distribution Pattern And Driving Factors Of Bacterial And Fungal Diversity In Lakes In The Middle And Lower Reaches Of The Yangtze River

As an interdisciplinary subject of ecology and geography,biogeography focuses on the distribution patterns and formation mechanisms of biodiversity along geographic gradients.It is one of the important contents in the field of ecology,and it is also one of the hot spots in the study of the response of ecosystem and biological community to environmental factors.Microorganisms are diverse and are an important part of the food web and biogeochemical cycles.They are sensitive to environmental changes and have strong adaptability and competitiveness in the environment.There are abundant microbial resources in lake water and surface sediments.To further explore the geographic distribution of microbial communities and their components in lakes and the mechanisms affected by environmental factors,identify key factors affecting bacterial and fungal community assembly,and tentatively explore the relative importance of environmental filtering and dispersal limitation in shaping microbial diversity patterns in freshwater lakes.This study can provide a scientific basis for the management and protection of lake ecosystems affected by climate change and human activities.In this paper,40 freshwater lakes distributed along the middle and lower reaches of the Yangtze River are studied.Taking spatial geographic distance as a typical gradient,the distribution patterns of biodiversity and community composition of different microbial groups(bacteria and fungi)along the geographic distance gradient and their relationship with environmental variables in 40 lake water and surface sediments were investigated by using high-throughput sequencing and biostatistics.To preliminarily explore the relative influence of deterministic process and random process in microbial assemblage change process.The main research results are as follows:(1)The abundance of bacteria and fungi in lake water and surface sediments was relatively high.A total of 57,686 bacterial OTU and 23,336 fungal OTU were obtained from the lake water samples.The Shannon-Wiener index of bacteria and fungi in lake water was 4.89 ± 0.45 and 4.60 ± 0.55,respectively.Proteobacteria(40.40%)and Actinobacteria(38.51%)were the most dominant phyla in the lake water.Other bacteria in lake water include Bacteroidetes(8.05%),Verrucomicrobia(4.26%),Cyanobacteria(2.62%),Planctomycetes(1.28%),etc.;Ascomycota(17.28%)was the dominant Eumycota in lake water.A total of 130,892 bacterial OTU and 24,734 fungal OTU were obtained from the surface sediments.The Shannon-Wiener index of bacteria and fungi in surface sediments was 7.93 ± 0.28 and 5.32 ± 0.63 respectively.Chloroflexi(17.07%)and Ascomycota(3.18%)showed the highest relative abundance of bacteria and fungi in surface sediments,respectively.(2)The fungi in lake water and the bacteria and fungi in surface sediments showed a predictable spatial distribution pattern,and their beta diversity showed a significant distance-decay relationship with the change of spatial geographical distance,that is,the community diversity increased significantly with the increase of distance.The bacterial beta diversity in lake water also increased with the increase of spatial distance,but it was not significant.Alpha diversity of bacteria and fungi in lake water and surface sediments did not show a strong distribution pattern along longitude and latitude gradients.(3)Environmental selection is an important factor affecting the diversity and community construction of bacteria and fungi in different habitats.The results showed that p H,ammonia nitrogen and dissolved oxygen had important effects on the bacterial alpha diversity in the water.Alpha diversity of fungi in lake water was strongly affected by p H and metal ions.The influence of spatial distance on bacteria in lake water was not significant,but the water depth,transparency and chlorophyll a content played an important role in community composition.In the surface sediments,the metal element(PC1),the metal-like element(As)and the electrical conductivity element(SPC)had a very important effect on the diversity and community composition of bacteria and fungi.(4)Mantel and Partial Mantel tests showed that environmental filtering and dispersal limitation jointly affected the community construction process of bacteria and fungi in different habitats.Mantel test showed that the community difference of fungi increased with the increase of spatial distance and environmental distance,while the community difference of bacteria only increased with the increase of environmental distance.The community differences of bacteria and fungi in lake surface sediments increased significantly with the increase of spatial distance and environmental distance.Partial Mantel test showed that the pure effect of environment on bacteria in water was stronger,while the pure effect of space distance on fungi in sediments was stronger.In summary,there are predictable spatial distribution patterns of fungi in lake water and bacteria and fungi in surface sediments.Environmental filtering and geographic distance play key roles in biodiversity and community assembly.