Response Of Soil Microbial Community To Nitrogen Addition In Alpine Wetland

Nitrogen deposition is an important part of global climate change.It affects soil nutrients and changes the use of soil microorganisms,thereby changing the structure and diversity of soil microbial communities.As an ecologically fragile area and sensitive area of global change,it is of great significance to explore the mechanism of alpine wetland ecosystem in response to global climate change.This study was carried out in the wetland-Xiaopo Lake alpine wetland of Qinghai Lake basin.A field simulated nitrogen addition experiment was conducted with NH₄NO₃ as nitrogen source.Three nitrogen addition gradients(N2:2 g/m²,N5:5 g/m²,N10:10 g/m²)and a blank control treatment(N0:0 g/m²)were set up,and three replicate experiments were set up in each treatment.Combined with high-throughput sequencing technology,the response mechanism of nitrogen addition was explored in terms of the quantitative community structure and diversity of soil microbial groups with different physical and chemical indexes.The main research results are as follows:(1)Effect of nitrogen addition on soil physicochemical propertiesSoil water content generally showed a downward trend under nitrogen application;Soil p H significantly increased under nitrogen addition;Soil total carbon,organic carbon,ammonia nitrogen and total nitrogen content decreased,and the highest nitrogen treatment significantly reduced the total carbon content in 15-30 cm soil layer;Nitrogen application increased nitrate content,and reached a significant level under the highest nitrogen treatment in 0-15 cm soil layer.Soil water content is the main influencing factor of soil total nitrogen and organic carbon.Soil inorganic nitrogen has no significant correlation with other physical and chemical properties,and the extremely significant correlation exists between soil total nitrogen,total carbon and organic carbon.(2)Effects of nitrogen addition on soil microbial biomassThrough the culture experiment,the results showed that the addition of nitrogen increased the number of soil bacteria,and the most obvious under N5 treatment.The number of soil fungi did not change significantly under N addition conditions;The number of soil actinomycetes decreased and the effect was not significant.(3)Effects of nitrogen addition on soil microbial community structure and diversitySequencing results showed that Proteobacteria(31.82%-43.50%),Chloroflexi(14.46%-17.36%),Acidobacteria(10.65%-18.87%)and Actinobacteria(9.90%-13.10%)were dominant in the bacterial community.The dominant fungi were Ascomycota(43.34%-68.15%)and Basidiomycota(3.84%-5.97%).The dominant archaeal phyla are Verrucomicrobia(22.16%-25.76%),Euryarchaeota(13.11%-22.43%),Crenarchaeota(8.76%-23.32%)and Thaumarchaeota(7.73%-10.86%).Under nitrogen addition,the relative abundance of Acidobacteria,Ascomycota,Euryarchaeota and Thaumarchaeota increased,while the relative abundance of Actinobacteria and Crenarchaeota decreased.Based on the results of microbial?diversity,it was found that the Chao1 index and Simpson index of soil bacteria did not change significantly,but the Shannon index increased and reached a significant level under N10 treatment,and the soil bacterial diversity increased.The?diversity index of soil fungi did not change significantly.The Chao1 index of soil archaea decreased,but the change was not significant,and the Simpson index and Shannon index did not change significantly.(4)Effect of nitrogen addition on AOAThe species of ammonia oxidizing archaea(AOA)were analyzed at the taxonomic level,and the following five genera were obtained,The relative abundance of Nitrosoarchaeum was 8.75%–23.10%,the relative abundance of Candidatus?Nitrosocaldus was 0.87%–10.05%,the relative abundance of Candidatus?Nitrosocosmicus was 2.37%–7.09%,the relative abundance of Nitrosopumilus was0.38%–7.03%,and the relative abundance of Nitrososphaera was 0.14%.According to UPGMA cluster tree and histogram,the community structure of AOA changed significantly.?diversity showed that Chao 1 index of ammonia-oxidizing archaea(AOA)increased under N2 and N10 treatments,but the effect was not significant,and decreased under N5 treatment,and reached a significant level.Simpson index increased and then decreased under nitrogen addition,reaching the highest value under N2 treatment and the lowest value under N5 treatment.There was no obvious linear trend in the change of Shannon index.The highest value was at N2treatment,and the lowest value was at N10 treatment,and the change was significant.(5)Effects of soil physical and chemical properties on soil microbial community structureRedundancy analysis of soil microbial community and dominant phyla of physical and chemical properties showed that the main influencing factor of bacterial community was soil organic carbon.With the increase of soil organic carbon,total carbon,total nitrogen and ammonium nitrogen content,the relative abundance of Proteobacteria and Chloroflexi increased,but the soil p H and nitrate nitrogen content and the relative abundance of Acidobacteria and Actinobacteria decreased.Soil p H and nitrate nitrogen were the main influencing factors of fungal dominant phylum.The increase of soil p H and nitrate nitrogen content increased the relative abundance of Ascomycota and Basidiomycota,and reduced the contents of total nitrogen,total carbon,organic carbon and ammonium nitrogen in soil.The main influencing factor of archaea community was soil total nitrogen content.The increase of relative abundance of Crenarchaeota was related to the increase of soil total nitrogen,total carbon,organic carbon and ammonium nitrogen content.