Effects Of Simulated Wet Deposition Of Nitrogen And Phosphorus And Litter Treatment On Soil Total Nitrogen And Organic Nitrogen In Korean Pine Forest

Since the industrial Revolution,human activities have caused global climate change.With the rapid development of industrialization,the continuous increase of atmospheric nitrogen deposition has seriously affected the structure and function of forest ecosystem.Litter is the main form of returning plant nutrients to soil,and litter yield and decomposition rate have an important impact on the nutrient balance of forest ecosystem.Therefore,forest litter is of great significance to the maintenance of forest soil fertility.In this paper,two forest types of Korean pine plantation and broadleaved Korean pine plantation on the southern slope of Liangshui Nature Reserve of Northeast Forestry University in Dailing District,Yichun City,Xiaohingan Mountains were selected as objects.The effects of wet deposition of N and P and litter treatment on soil total N and organic N were studied by combining plot setting and investigation,experimental design,soil sample collection and determination,and statistical analysis.The experimental design is as follows:（1）nitrogen and phosphorus deposition experiment,using（NH₄）₂SO₄and（NH₄）₂HPO₄as nitrogen source and phosphorus source to conduct simulated nitrogen and phosphorus deposition experiment from May to September 2018 and 2019,respectively.Nitrogen and phosphorus deposition treatment is set at four levels:Low application rate(N 5 g m^-2a^-1,P 5 g m^-2a^-1),medium application rate(N 15 g m^-2a^-1,P 10 g m^-2a^-1),high application rate(N 30 g m^-2a^-1,P 20 g m^-2a^-1)and no application of N and P(N 0 g m^-2a^-1,P 0 g m^-2a^-1)（control）,each level had 3 replicates;（2）Litter fall treatment test.Litter fall treatment set three levels:keeping the original litter fall（control）,removing litter fall and adding litter fall,with three replicates for each level.In May,August and October of 2018 and 2019,three sampling sites of 30 cm×30 cm were randomly selected from each quadrats,and soil samples of 0～20 cm were collected from each sampling site.This study aims to provide scientific basis and data support for predicting the effects of nitrogen and phosphorus deposition and litter change on soil fertility of Korean pine forest ecosystem in this region in the future.The main results are as follows:（1）Under different nitrogen and phosphorus deposition and litter treatment,The contents of soil total nitrogen,soil hydrolyzed organic nitrogen and soil non-hydrolyzed organic nitrogen in broad-leaved Korean pine forest in the first year（2018）and the second year（2019）were significantly higher than those in Korean pine plantation,and the contents of soil total nitrogen,soil hydrolyzed organic nitrogen and soil non-hydrolyzed organic nitrogen in the second year were all higher than those in the first year.In the Korean pine plantation and broadleaved Korean pine plantation,there were significant differences in soil total nitrogen,acid hydrolyzed total nitrogen,amino acid nitrogen and ammonia nitrogen between 2018 and2019（P<0.05）,but there were no significant differences in amino sugar nitrogen,acidolysis unknown nitrogen and non-hydrolytic organic nitrogen（P>0.05）.（2）The contents of soil hydrolyzed organic nitrogen were as follows:total soil hydrolyzed nitrogen>Soil amino acid nitrogen>Soil ammonia nitrogen>Soil amino sugar nitrogen>Soil acid hydrolysis of unknown nitrogen,The contents of soil non-hydrolytic organic nitrogen were as follows:total nitrogen of soil humic acid>Soil rich acid nitrogen>Soil humic acid nitrogen.（3）Under different nitrogen and phosphorus deposition treatments,the contents of total hydrolyzed nitrogen,ammonia nitrogen,humic acid nitrogen,fulic acid group nitrogen,humic acid group nitrogen（P<0.05）;the contents of amino acid nitrogen and amino sugar nitrogen in soil were significantly increased by medium concentration treatment（P<0.05）;high concentration treatment significantly increased the contents of total hydrolyzed nitrogen,ammonia nitrogen,amino acid nitrogen,amino sugar nitrogen and unknown acid hydrolyzed nitrogen（P<0.05）.（4）Under different litter fall treatments,the contents of soil ammonia nitrogen,amino sugar nitrogen,soil humic acid nitrogen and humic acid nitrogen were the highest in undisturbed litterfall treatments,and the contents of soil acid hydrolyzed total nitrogen and amino acid nitrogen（P<0.05）;litter removal treatment could significantly increase the contents of total nitrogen,amino acid nitrogen and ammonia nitrogen（P<0.05）.（5）In the first year of the experiment（2018）,the interaction of sampling month,forest type,N and P deposition and litter treatment had significant effects on soil total N and acid hydrolyzed total N（P<0.05）,the sampling month,N and P deposition and litter treatments had significant effects on soil total nitrogen,soil acid hydrolyzed total nitrogen and soil ammonia nitrogen（P<0.05）,litter treatment had significant effects on soil total nitrogen,soil acid hydrolyzed total nitrogen and soil amino acid nitrogen（P<0.05）,nitrogen and phosphorus deposition had significant effects on soil total nitrogen and total nitrogen by acid hydrolysis（P<0.05）;in the second year of the experiment（2019）,the interaction of sampling month,forest type,N and P deposition and litter treatment only had significant effects on soil amino sugar nitrogen（P<0.05）.N and P wet deposition and litter are closely related to soil fertility and plant growth.In this paper,the effects of simulated wet deposition of nitrogen and phosphorus and litter treatment on soil organic nitrogen in broad-leaved Korean pine and Korean pine plantations were analyzed,including total nitrogen,hydrolyzed organic nitrogen and non-hydrolyzed organic nitrogen,However,there is a lack of studies on the impact of precipitation,temperature and other climate factors on soil organic nitrogen in Korean pine forest.In the future,in-depth studies will be conducted on the influencing factors of soil organic nitrogen in Korean pine forest.