Soil Fungal Community Structure And Diversity In Response To Nitrogen Addition And Increased Precipitation In A Stipa Baicalensis Meadow Steppe

Atmospheric nitrogen deposition and changes in precipitation regimes cause a great influence on the structure and function of grassland ecosystem.There are widespread concern and deep study focus on the effects of nitrogen deposition and increased precipitation on the plant community structure and plant diversity of grassland ecosystem.However,lack of knowledge on the microbial communities in grassland soil,especially,the mechanism and varying patterns of fungal community structure and diversity.This study conducted an in situ experiment with nitrogen addition,increased precipitation and combined their effects on the Stipa baicalensis meadow steppe.Concretely,nitrogen additive amount was 50 kg N hm-2yr-1by NH4NO3,and increased 1/7 natural precipitation by the appliance of intercept rainfall.We sampled the soil four times during the growing seasons and measuring the quantitative characteristics of plant community.Moreover,we expounded the response of soil fungal community structure and diversity to nitrogen addition and increased precipitation through high-throughput sequencing and real-time PCR.The specific questions addressed were:(1)whether nitrogen addition,increased precipitation and their interactions influence the fungal community structure and diversity on Stipa baicalensis meadow steppe;(2)the seasonal dynamics of the fungal community structure and diversity on Stipa baicalensis meadow steppe;and(3)the main environment factors in affecting the fungal community structure and diversity on Stipa baicalensis meadow steppe.The mainly results are as follow:(1)18S rRNA high throughput sequencing of soil fungal communities showed that there are 32 phyla,55 classes,90 orders,115 families and 154 species on Stipa baicalensis meadow steppe.The dominant fungal communities are Ascomycota and Basidiomycota.The relative abundance of four classes are more than 10% in the 16 dominant classes.They are Sordariomycetes,Eurotiomycetes,Dothideomycetes,and Agaricomycetes,and the relative abundance are 17.99%,14.24%,13.95% and 13.77%,respectively.(2)Nitrogen addition significant reduce the soil fungal biomass C,N(P(27)0.05),whereas has no significant effects on soil fungal community structure and diversity.Increased precipitation could partly remit the inhibiting effect of nitrogen addition on soil fungi.Nitrogen addition and increased precipitation had interactive effects on the soil fungal diversity index in the different month.In addition,there are major differences of relative abundance in the most dominant classes(especially the class which belong to Ascomycota)with changes in month.(3)The Ace index,Chao index and Shannon index of soil fungi are significant difference in the different period during the growing seasons.The relative abundance of Glomeromycota incertae sedis,Leotiomycetes,Zygomycota_incertae_sedis,Orbiliomycetes,Tremellomycetes,Chytridiomycota incertae sedis,Microbotryomycetes and Intramacronucleatad had significant differences in different month.In sum,there were obviously seasonal dynamic of soil fungal community structure.(4)The ratio of soil bacteria to fungi showed a monthly dynamic regularity obviously.Concretely,the ratio of soil bacteria to fungi was highly in August compared to other month.However,there was no significant change in soil fungal abundance in August.Therefore,the changes in the ratio of soil bacteria to fungi are mainly due to the variance in soil bacterial abundance.In addition,the interactive effects of nitrogen addition and increased precipitation were significant reduce the soil fungal abundance,which caused the rise in the ratio of soil bacteria to fungi.(5)The analysis of environment factors showed that the mainly driver factor in affecting soil fungal community structure was soil total nitrogen.Soil total nitrogen has significant positive correlations with the relative abundance of Dothideomycetes,Zygomycetes and Chytridiomycetes,and has significant negative correlations with the relative abundance of Glomeromycetes and Agaricomycetes.Thus,the indirect effects of nitrogen addition and increased precipitation on soil fungal community structure and diversity might through affecting the plant species richness.In sum,the effects of nitrogen addition and increased precipitation on soil fungal community structure and diversity are weaker than the seasonal dynamic of soil fungi on Stipa baicalensis meadow steppe.It implied that the mainly reasons in regulating the soil fungal community structure and diversity are the variations of seasonal precipitation regime and plant species richness.This study suggested that the effects of atmospheric nitrogen deposition and changes in precipitation regime on microbial communities in grassland soil,may be a slowly and complex ecological process.It is important to extend the temporal scale of simulated global change monitoring.