Response Of Soil Respiration To Short-Term Simulated Nitrogen Deposition In Quercus Acutissima Forest Along Urban-Rural Environmental Gradient

Human activities,the use of fossil fuels and chemical fertilizers will produce a large number of nitrogen-carbon element gases,and some of the nitrogen-containing gases(CO₂ and NO_x)will destroy the carbon and nitrogen balance of forest ecology.Soil respiration plays an important role in forest ecosystem.Under the background of rapid increase of global N deposition,understanding the mechanism of soil respiration and soil composition on N deposition can better cope with the impact of rapid increase of N deposition on forest ecosystem.In this paper,experimental data collection from August2020 to December 2020(Growing season:August;Late growing season:October;Non-growing season:December),from the perspective of urban and rural environmental gradient,Quercus acutica forest as the research object,selected similar site conditions to establish a sample plot in Hefei(Urban Forest:Dasu Mountain Forest Park;Suburban Forest:Zipeng Mountain National Forest Park),Lu'an Shucheng(Rural natural forest:Wanfo Mountain National Forest Scenic Spot)area,to conduct simulated nitrogen deposition experiment.Three nitrogen application treatments were set up on the plot,namely control(CK,0kg N ha^-1yr^-1),low nitrogen(LN,50kg N ha^-1yr^-1),and high nitrogen(HN,100kg N ha^-1yr^-1),to study the effects of nitrogen deposition on the forest soil respiration and composition of urban and rural environmental gradients,and measure soil temperature and humidity and soil physical and chemical properties indicators to analyze urban and rural environmental gradients Soil respiration and its component differences and their influencing factors can more accurately monitor the response of forest ecosystems to nitrogen deposition,and provide a scientific reference for formulating policies and guidelines on environmental issues.The main research results are as follows:(1)The effect of urban and rural environmental gradient on soil respiration.The seasonal distribution of soil respiration and components in urban and rural environmental gradients was higher in summer and lower in winter.On the rural-urban environmental gradient,soil respiration and its components were as follows:soil respiration(Rs):urban>suburban>village,heterotrophic respiration(Rh):urban>rural>suburban,and autotrophic respiration(Ra):suburban>urban>rural.(2)Effects of nitrogen deposition on soil respiration and soil composition in urban and rural gradient environments.The effects of nitrogen deposition on soil respiration and composition of urban and rural environmental gradients are mainly in the growing season.Nitrogen application has an inhibitory effect on soil respiration in urban and rural environmental gradients.The contribution rates of heterotrophic respiration in urban forest,suburban forest and rural natural forest were 58.25%?82.22%,29.26%?63.82%and 49.46%?76.63%,respectively.Nitrogen application could affect the proportions of heterotrophic respiration and autotrophic respiration.(3)The relationship between soil temperature and humidity and soil respiration and components in urban and rural environmental gradients.The correlation between soil temperature and heterotrophic respiration in urban and rural environmental gradients is greater than that between soil respiration and temperature.Compared with soil moisture,soil temperature has a better correlation with soil respiration and composition.The synergistic effect of soil temperature and humidity can explain Rs better than a single factor.The Q₁₀ value has obvious characteristics of urban-rural environmental gradient change,which is expressed as:city>urban>rural.(4)Effects of nitrogen deposition on soil physical and chemical properties.Nitrogen application promoted the contents of MBC,MBN,NH₄⁺-N and NO₃^--N in the gradient soil of urban and rural environment,but had no obvious effects on p H,TN,TC and C/N in the gradient forest soil.(5)Correlation of soil respiration and components with soil physical and chemical properties in urban and rural environmental gradients under nitrogen deposition.There were significant correlations between MBN,TDN,TC,C/N and soil respiration and components in urban and suburban forests(p<0.05).The physical and chemical properties of rural natural forest and soil showed negative correlation.