Effects Of Nitrogen Addition On Litter Decomposition And Soil Properties Under The Forest Of Picea Schrenkiana In Tianshan Mountain,Xinjiang

Since the Industrial Revolution,human activities such as the combustion of fossil fuels,the use of nitrogen-containing chemical fertilizers and the rapid development of animal husbandry have led to a surge in the content of active nitrogen in the atmosphere.As a result,the content of nitrogen entering the ecosystem has far exceeded the demand for nitrogen in the system,and the ecological effects of excessive nitrogen deposition have become the focus of research all over the world.At present,China has become one of the three major nitrogen deposition concentration areas in the world,and will become the fastest increasing area of nitrogen deposition in the world.Studies at home and abroad have shown that these increased exogenous nitrogen inputs have had an impact on litter decomposition and soil properties in temperate and tropical and subtropical ecosystems in humid and semi-humid areas.However,at present,the research on whether the addition of exogenous nitrogen affects the litter-soil relationship of temperate forest ecosystem in arid area is relatively insufficient.In view of the above problems,this study took the forest of Picea schrenkiana in Tianshan,Xinjiang,as the research object,and systematically studied the litter decomposition under the forest of Picea schrenkiana and the response of soil properties under the forest to the addition of exogenous nitrogen by in situ method.The purpose of this study was to investigate the effects of different levels of exogenous nitrogen on the decomposition rate and matrix quality under the forest of Picea schrenkiana,and to compare the effects of different levels of exogenous nitrogen on soil properties under the forest of Picea schrenkiana in Tianshan,Xinjiang.The effects of different levels of exogenous nitrogen on the relationship between litter and soil in Tianshan forest ecosystem were clarified.The main results of the study are as follows.1.In this study,it was found that the treatment of the low nitrogen group?N₁?and the medium nitrogen group?N₂?promoted the litter decomposition under the forest of Picea schrenkiana in Tianshan,Xinjiang,while the high nitrogen group inhibited the litter decomposition.2.The Oldson model fitting of the litter decomposition rate under the forest of Picea schrenkiana in Tianshan,Xinjiang,can be seen that with the increase of nitrogen application rate,the annual decomposition coefficient k of the litter under the forest of Picea schrenkiana in Tianshan,Xinjiang,shows a trend of increasing first and then decreasing,the specific range is 0.352⁰.599.The fitting equation of the control group?N₀?is y=104.378e^-0.428x,the fitting equation of the low nitrogen group?N₁?is y=106.723e^-0.599x,and the fitting equation of the medium nitrogen group?N₂?is y=103.716 e^-0.523x,the fitting equation of the high nitrogen group?N₃?is y=101.404e^-0.352x.The time required to litter under the forest of Picea schrenkiana in Tianshan,Xinjiang,decomposed 50%and 95%is1.720².009a and 7.099⁸.550a,respectively.3.The addition of exogenous nitrogen has different effects on the elements and the chemical composition and the ecological stoichiometric ratio of litter under the forest of Picea schrenkiana in Tianshan,Xinjiang.Nitrogen addition treatment weakened the release of carbon in litter,and increased the nitrogen content of litter.However,no effect of nitrogen addition on litter phosphorus,but the overall performance was negative.Low nitrogen group promoted the decomposition of lignin in litter,and high nitrogen group significantly inhibited the degradation process of lignin.Compared with the control group?N₀?,the nitrogen addition treatment promotes the decomposition of cellulose in the litter.In litter decomposition,C/N and P/N under the low nitrogen group?N₁?and medium nitrogen group?N₂?were lower than control group,but the higher than the control group?N₀?under high nitrogen group?N₃?;lignin/cellulose in litter under nitrogen addition treatment was higher than the control group?N₀?.4.The addition of exogenous nitrogen changed the relationship between soil physical and chemical properties and enzyme activities under the forest of Picea schrenkiana in Tianshan,Xinjiang.The important order of soil physical and chemical properties on the characteristics of soil enzyme activity of the control group?N₀?is soil electroconductibility?S_EC?>soil total phosphorus?S_TP?>soil bulk density?S_BD?>soil total nitrogen?S_TN?>soil water content?SWC?>soil ammonium nitrogen?S_NH₄⁺?>soil organic carbon?SOC?>soil pH.The important order of soil physical and chemical properties on the characteristics of soil enzyme activity of the low nitrogen group?N₁?is soil electroconductibility?S_EC?>soil water content?SWC?>soil bulk density?S_BD?>soil organic carbon?SOC?>soil total nitrogen?S_TN?>soil total phosphorus?S_TP?>soil ammonium nitrogen?S_NH₄⁺?>soil pH.The important order of soil physical and chemical properties on the characteristics of soil enzyme activity of the medium nitrogen group?N₂?is soil ammonium nitrogen?S_NH₄⁺?>soil bulk density?S_BD?>soil pH>soil total phosphorus?S_TP?>soil total nitrogen?S_TN?>soil organic carbon?SOC?>soil electroconductibility?S_EC?>soil water content?SWC?.The important order of soil physical and chemical properties on the characteristics of soil enzyme activity of the high nitrogen group?N₃?is soil pH>soil water content?SWC?>soil bulk density?S_BD?>soil total nitrogen?S_TN?>soil organic carbon?SOC?>soil electroconductibility?S_EC?>soil total phosphorus?S_TP?>soil ammonium nitrogen?S_NH₄⁺?.5.Under the treatment of different exogenous nitrogen addition concentrations,the main factors affecting the decomposition characteristics of litter under the forest of Picea schrenkiana in Tianshan,Xinjiang,are different.The major factors of the control group?N₀?were soil organic carbon?SOC?and soil protease activity?S_PR?;the major factors of the low nitrogen group?N₁?were soil pH and soil acidic phosphatase activity?S_ACP?;the major factor of the medium nitrogen group?N₂?was soil pH and soil urease activity?S_UR?;the major driving factors for the high nitrogen group?N₃?are soil pH and soil protease activity?S_PR?.