Response Of Soil Main Microbial Groups And Enzyme Activities To Simulated Nitrogen Deposition In Subalpine Coniferous Forests Of Western Sichuan

Nowadays,the increase of global atmospheric nitrogen deposition has become very obvious.China has become the third largest nitrogen deposition area after Europe and America.The increase of atmospheric nitrogen deposition will bring about a series of ecological problems such as acidification of soil and water quality and changes in biodiversity.Extracellular enzymes secreted mainly by soil microorganisms are important catalysts and actively participate in various biochemical processes in the soil.Soil microbes are sensitive to changes in environmental factors.Simulating nitrogen deposition experiments in subalpine forest ecosystems to study soil biochemical processes is important for understanding the effects of increased atmospheric nitrogen deposition on material circulation and energy flow in subalpine forest ecosystems.However,the results of the study on simulated microbial sedimentation on soil microbial populations and enzyme activities are inconsistent,and mainly focus on temperate forest ecosystems,and there is a lack of research on nitrogen-limited mountain forests in western Sichuan.Therefore,will the increase of atmospheric nitrogen deposition significantly change the soil microbial population,will it significantly change the soil enzyme activity and stoichiometry,and thus affect the carbon,phosphorus and phosphorus cycle of the soil?Based on this,we selected the Sichuan Redwoods?Larix mastersiana?plantation in the high mountains of Western Sichuan as the research object,through four horizontal gradient soil nitrogen control experiments(CK:0 g m^-2 a^-1,N1:2 g m^-2 a^-1,N2:5 g m^-2 a^-1,N3:10 g m^-2 a^-1),using a phospholipid fatty acid analysis method and an improved method by Bob Sinsabaugha Lab,studied subalpine the microbial population of forest soil,soil extracellular enzyme activity and stoichiometry and the relative limitation of soil microbes to carbon,nitrogen and phosphorus,to explore the response of soil biochemical processes to simulated nitrogen deposition in the context of future climate change.Simulated nitrogen deposition had a significant effect on soil gram-positive bacteria?P<0.05?,bacterial content,fungal content,gram-negative bacteria content,total microbial content,fungal/bacterial ratio,gram-negative bacteria/gram There was no significant effect on the positive bacteria?P>0.0.5?,and simulated nitrogen deposition did not significantly change the soil microbial content and group structure.The sampling time had a significant effect on soil microbial content and group structure?P<0.01?.Soil soluble carbon,phosphorus and inorganic nitrogen,temperature and water content are the main soil physical and chemical factors affecting the microbial population changes.Soil extracellular enzyme activity is closely related to soil microbial population changes,and the correlation between Gram-negative bacteria and soil enzyme activity was most notable.Simulated nitrogen deposition significantly promoted N-acetylglucosidase and peroxidase activities?P<0.01?,and the degree of N2 treatment was higher than that of N1 and N3.Simulated nitrogen deposition had a significant effect on C:N_EEA,N:P_EEA,and microbial relative nutrient limitation?P<0.01?.Soil carbon and nitrogen restriction were alleviated to some extent,especially N2 treatment was more obvious,and under N2 treatment transfer from nitrogen to phosphorus limit.The sampling time had a significant effect on soil enzyme activity and stoichiometry,and microbial relative nutrient limitation?P<0.01?.Soil enzyme activity and stoichiometry were negatively correlated with soil temperature;soil enzyme activity and stoichiometry related to carbon conversion were negatively correlated with soil water content,and soil enzyme activity and soil moisture content related to nitrogen and phosphorus transformation.There was a positive correlation;most soil enzyme activities and stoichiometry were not significantly correlated with soil pH;most soil enzyme activities were positively correlated with soil soluble carbon,while stoichiometry was negatively correlated;soil enzyme activity and stoichiometry,the relative nutrient limitation of microorganisms was significantly correlated with soil inorganic nitrogen and soluble phosphorus.The main physical and chemical factors affecting soil enzyme activity are soil soluble carbon,phosphorus,inorganic nitrogen,temperature and water content.In summary,simulated nitrogen deposition has little effect on soil microbial groups,and N-acetylglucosidase and peroxidase activities are significantly promoted?P<0.01?.Simulated nitrogen deposition alleviated carbon and nitrogen confinement in the study area and restricted nitrogen transfer to phosphorus under N2 treatment.Seasonal changes have significant effects on soil microbial and enzyme activities and soil physical and chemical properties.Soil soluble carbon,nitrogen and phosphorus are the main factors affecting soil microbial groups.These findings will provide a reference for understanding the process of soil ecosystems in subalpine forests under atmospheric nitrogen deposition.