Response Of Microbes In The Rhizosphere To Nitrogen Addition In A Broad-leaved Korean Pine Forest In The Xiaoxing'an Mountains

Nitrogen deposition is one of the hotspots of research affecting ecosystem stability,affecting rhizosphere microbial diversity and community structure,but the effects on the functional groups of rhizosphere microbes need further study.In this paper,the effects of nitrogen application on the rhizosphere microorganisms of the dominant tree species（Acer tegmentosum Maxim and Korean pine）in Xiaoxingan Ridge were investigated in depth by the r RNA genome sequencing technique,providing a reference for exploring the rhizosphere microbial diversity,community structure and functional groups in response to nitrogen deposition in boreal temperate forests.The 4 nitrogen levels were control group(CK,0 g N m~2·yr^-1),low nitrogen treatment(LN,2.5 g N m~2·yr^-1),medium nitrogen treatment(MN,5 g N m~2·yr^-1),and high nitrogen treatment(HN,7.5g N m~2·yr^-1).The results are as follows:（1）Nitrogen application significantly altered the rhizosphere bacterial diversity of Acer tegmentosum Maxim（P<0.01）,but had no significant effect on rhizosphere fungal diversity of Acer tegmentosum Maxim or rhizosphere bacterial and fungal diversity of Korean pine.The community structure of rhizosphere fungi in Acer tegmentosum Maxim changed significantly due to nitrogen addition（P<0.05）,which was mainly related to the effect of nitrogen application on mycorrhizal symbioses,saprophytes and pathogens.In addition,there were no significant changes（P>0.05）in the structure of the rhizosphere bacterial and fungal communities of Acer tegmentosum Maxim,and Korean pine（P>0.05）.（2）The structure of the rhizosphere microbial functional groups of the two tree species did not change significantly（P>0.05）,but some rhizosphere microbial functional groups were significantly affected by nitrogen addition.The strongest response of the rhizosphere bacterial functional groups of Acer tegmentosum Maxim included aerobic＿ammonia＿oxidation,nitrification,respiration＿of＿sulfur＿compounds,sulphate＿respiration,ureolysis,etc.,and some saprophytic bacteria.（3）Combining environmental factors with rhizosphere microbiota of Acer tegmentosum Maxim and Korean pine,we found that:soil total carbon（TC）,total nitrogen（TN）and total organic carbon（TOC）drove changes in the structure of rhizosphere fungal communities in Acer tegmentosum Maxim;soil p H,total carbon（TC）and total nitrogen（TN）were significantly associated with rhizospheric Biomarker species of Acer tegmentosum Maxim,and soil p H,total carbon（TC）,total nitrogen（TN）and ammonium nitrogen（NH₄⁺-N）influenced the rhizosphere functional groups of Acer tegmentosum Maxim.There were fewer Korean pine rhizospheric Biomarkers compared to Acer tegmentosum Maxim,and the smaller effect of nitrogen application on Korean pine rhizosphere microbes may be related to the tree species,making rhizosphere microbes and Korean pine roots more resilient in a process of mutual selection and adaptation.Therefore,exploring the response of soil microorganisms to nitrogen deposition needs to take into account the influence of tree species as well.