Structure And Assembly Mechanism Of Planktonic Fungal Communities In Subtropical Urban Lakes

Urban lakes,as small and medium-sized lakes in urban or suburban areas,are an important part of urban water environment,providing local residents with abundant freshwater resources and recreational places,which have important ecological and social service values.As a"rare species"of planktonic microorganisms,planktonic fungi play an important role in the carbon and nutrient cycles of lake ecosystems,and have important reference values in the biological monitoring of lake ecological health.Nanchang lakes are an important source of water for agriculture and industry in Nanchang and have been strongly influenced by human activities and urbanization in recent years.Previous studies on Nanchang lakes mainly included river water quality evaluation,lake area change and lake biology（phytoplankton,benthic animals and bacterioplankton）,and the formation mechanism of planktonic fungal communities in Nanchang lakes is not clear.In this study,seven lakes（Yao Lake,Aixi Lake,Qingshan Lake,Xiang Lake,Libu Lake,Kongmu Lake and Jiulong Lake）in Nanchang were selected and surface water samples were collected in three seasons:dry season,normal season and wet season.The physicochemical indexes of lake water were measured:p H,dissolved oxygen（DO）,water temperature（WT）,ammonia nitrogen（NH₄⁺-N）,nitrate nitrogen（NO₃^--N）,total organic carbon（DOC）,chromium（Cr）,cadmium（Cd）,arsenic（As）and lead（Pb）.The planktonic fungal communities in Nanchang lakes were determined by Illumina Miseq high-throughput sequencing platform,and the community structure and assembly mechanism of planktonic fungal communities were elucidated by using principal coordinate analysis（PCo A）,sequencing analysis（CCA）,network analysis and Stegen zero model analysis,in order to establish a biological indicator method for water quality in Nanchang urban lakes and provide a theoretical basis for water environmental protection in Nanchang urban lakes.The main findings are as follows The main conclusions are as follows.（1）A total of 11 phyla and 404 genera of planktonic fungi were identified in Nanchang lakes.Unclassified＿k＿Fungi had the highest relative abundance,accounting for 24.01-97.67%of the total community of the samples tested.The dominant phyla were Basidiomycota（0.25%～72.41%）,Chytridiomycota（0.00%～29.96%）,Rozellomycota（0.10%～10.84%）,Ascomycota(0.02%～（0.02%～11.32%）,Blastocladiomycota（0.00%～15.06%）and Mortierellomycota（0.00%～0.56%）.The top10 identified fungal genera in relative abundance included Cladosporium（0.00%-5.92%）,Aspergillus（0.00%-2.48%）,Alternaria（0.00%-1.56%）,Tausonia（0.00%-1.04%）and Betamyces（0.00%～2.48%）.（2）Among the dominant phyla,there were significant seasonal differences between Basidiomycota and Blastocladiomycota,and non-significant seasonal differences between Chytridiomycota,Ascomycota,Chytridiomycota and Ascomycota.The relative abundance of Basidiomycota and Blastocladiomycota was significantly higher in the wet season,and the trend was the same for both.Among the top 10identified fungal genera,Aspergillus,Tausonia and Betamyces showed significant seasonal differences in relative abundance,while Cladosporium and Alternaria showed insignificant seasonal differences.Among them,Aspergillus was significantly higher in the normal season,Tausonia was significantly higher in the wet season,and Betamyces was significantly higher in the dry season.（3）Theα-diversity（Shannon index,Chao1 index,Shannoneven index and pd index）and community stability of planktonic fungal communities in Nanchang Lake did not show significant differences between dry,normal and wet seasons,while theβ-diversity was significantly different between dry,normal and wet seasons.（4）Cr was the significant water physicochemical index affecting Shannoneven index and Shannon index,and WT was the significant water physicochemical index affecting Shannoneven index.cd and Pb were the significant water physicochemical indexes affecting community stability,and the stability of planktonic fungal community tended to decrease with the increase of Cd and Pb concentration in water.WT and DO were the main water physicochemical indicators affecting the seasonal variation of planktonic fungal communityβ-diversity,followed by p H,Cd,NH₄⁺-N and NO₃^--N.（5）The construction of planktonic fungal communities in Nanchang Lake was mainly dominated by deterministic processes（explaining 64.9%of the community variation）,including heterogeneous selection（62.9%）and homogeneous selection（2%）;stochastic processes explained 35.1%of the community variation,including homogenized diffusion（1%）,diffusion limitation（0.1%）and unclassified processes（34%）.（6）Abiotic factors（water physicochemical indicators）had more influence on planktonic fungal community construction than biotic factors（interspecific interactions）,where WT and Cd were the most significant factors affecting planktonic fungal community construction,followed by NO₃^--N,interspecific interactions and DO.