Effects Of Nitrogen Deposition On Soil Organic Carbon And Its Active Components In Urban And Rural Gradient Forest

Soil organic carbon and its active components can indicate soil fertility and carbon pool changes and play an important role in soil nutrient cycling.In recent years,rapid urbanization has directly and indirectly affected the structure and function of forest ecosystems in and outside urban areas,and led to obvious gradient changes of ecological environment elements between urban and rural areas.At the same time,since the industrial Revolution,nitrogen deposition has become another important factor affecting the carbon cycle of forest soil in modern times.Due to the different background values of forest ecological environment elements on the urban-rural gradient,there may be differences in the feedback of nitrogen deposition,but there is still a lack of systematic research on this aspect.Therefore,it is of great significance to study the temporal and spatial distribution characteristics of soil organic carbon and its active components and its response to nitrogen deposition in urban and rural gradient forest soil.This study was carried out in the typical urban and rural gradient forest plots established by the team,namely,Urban forest plots,Suburban forest plots,and Rural forest plots.Through simulated nitrogen deposition experiment,three treatment levels of control,low nitrogen and high nitrogen(0,50 and 100 kg N·ha^-1·yr^-1)were set in each plot.At the same time,the soil physical and chemical indexes in the sample plots were determined to explore the driving factors affecting the forest soil organic carbon and its active components under nitrogen deposition.The results are as follows:（1）In terms of space,the Soil organic carbon（SOC）,Microbial biomass carbon（MBC）and Easy–oxidized organic carbon（EOC）contents of urban and rural forest soil were as follows Rural Forest>Urban Forest>Suburban Forest,the Dissolved organic carbon（DOC）content is as follows Suburban Forest>Urban Forest>Rural Forest.In terms of time,month had a significant effect on forest soil organic carbon and its active components in urban and rural gradient.The seasonal distribution characteristics were generally high in summer and low in winter,and July 2021 was significantly higher than other months.The contents of soil organic carbon and its active components decreased with the increase of soil depth.（2）The distribution ratios of soil dissolved organic carbon（DOC/SOC）,microbial biomass carbon（MBC/SOC）and Easy–oxidized organic carbon（EOC/SOC）are significantly different under the urban-rural gradient,and the overall performance is Suburban Forest>Urban Forest>Rural Forest.Urban Forest N addition increased soil DOC/SOC,MBC/SOC,EOC/SOC,while rural forest N addition decreased soil DOC/SOC,MBC/SOC,EOC/SOC.Suburban forests increased soil DOC/SOC,MBC/SOC,EOC/SOC under LN treatment,and decreased under HN treatment.In this study,the ratio of easily oxidized organic to total organic carbon was the largest,the ratio of Dissolved organic carbon was the second,and that of microbial biomass was the smallest.（3）Nitrogen deposition had significant effects on soil organic carbon and its active components.In the Urban Forest,n deposition increased soil SOC,DOC,MBC and EOC under LN treatment,but decreased under HN treatment;Nitrogen deposition increased soil SOC and EOC,but decreased soil DOC,soil MBC increased under LN treatment and decreased under HN treatment in suburban forest;In rural forests,nitrogen deposition increased soil SOC,DOC,MBC and EOC.（4）Soil physicochemical properties and active carbon components accounted for 91%,61%,60%and 82%of soil SOC,DOC,MBC and EOC.TN,p H,MBN and SOC were the main driving factors of soil SOC,DOC,MBC and EOC.In conclusion,urban forest soil organic carbon and its active components have significant differences in urban and rural gradient,and there are differences in the response of urban and rural gradient forests to nitrogen deposition,and the main driving factors affecting soil organic carbon and its active components are also different.This study provides a scientific basis for further understanding the nutrient cycling process of rural-urban gradient forests and theoretical support for ecological risk assessment of regional urbanization process.