Effects Of Nitrogen Deposition On Soil Respiration Of Natural Secondary Forest In Changbai Mountain

Nitrogen deposition changes the process of soil carbon cycling,which in turn destroys the stability of forest ecosystems.Soil respiration is mainly composed of soil microbial respiration,plant root respiration,etc.With the increase of atmospheric nitrogen deposition,studying the response of soil respiration components to nitrogen deposition and exploring its impact mechanism is of great significance for a deep understanding of the carbon dynamics of forest ecosystems.This study takes the typical natural secondary forest in the northeast region as the research object.Simulated nitrogen deposition experiment of Poplar-Birch Secondary Forest in Changbai Mountain-Jilin province from May 2017 to October 2017.A total of three treatment levels are set for this experiment:Control treatment(0 gN?m^-2?a^-1),low nitrogen treatment(2.5 gN?m^-2?a^-1)and high nitrogen treatment(5.0 gN?m^-2?a^-1).The effects of nitrogen deposition on soil respiration components and the basic physicochemical properties of soil in secondary forests were studied,and the effect of litter treatment on soil respiration was also studied.The results of the study are as follows.?1?Nitrogen deposition significantly reduced soil pH in the secondary forest of Changbai Mountain,and soil total nitrogen content increased significantly.At the same time,nitrogen deposition also has a significant effect on soil DON,DOC,and some of soil metal elements.?2?Nitrogen deposition changes the correlation between basic physical and chemical properties of soil and metal elements in soil.It may be due to nitrogen deposition that affects the absorption and utilization of various elements by plants and microorganisms,and at the same time changes the coupling and uncoupling between elements.?3?Nitrogen deposition had extremely significant effects on Rl,Rr,Rs,and Rt,and the monthly differences in soil respiration components were also significantly different.At the same time,nitrogen treatment and month interactions were also significant impact for Rt,Rs,Rr,and Rl.In the control plots throughout the growing season,Rl accounted for 20%,Rr accounted for 28%,Rs accounted for 52%;low nitrogen treatment Rl accounted for 23%,Rr accounted for 28%,Rs accounted for 49%;high nitrogen treatment Rl accounted for 21%Rr accounts for 29%and Rs accounts for50%.It can be seen that low-nitrogen treatment has a certain role in promoting R1 and Rs throughout the year,and high-nitrogen treatment has a certain inhibitory effect on Rr throughout the year.?4?Decreasing litter in control plots non-significantly influence soil respiration in May and June,and significantly inhibited soil respiration in the rest of the month;decreased litter had a significant inhibitory effect on soil respiration in low-nitrogen treatment levels in May?June?July?August and September;decreased litter had a significant inhibitory effect on soil respiration in high-nitrogen treatment levels in July?AugustSeptember and October.In short,decreasing litter has a certain inhibitory effect on soil respiration.The control,low nitrogen treatment and high nitrogen treatment were reduced by 14.5%,25.1%and 19.9%respectively.?5?Nitrogen deposition and litter treatment both alter the temperature sensitivity of soil respiration.Control treatment showed:Normal Litter>Add Litter>Decrease Litter;Low Nitrogen treatment Shows:Add Litter>Normal Litter>Decrease Litter;High Nitrogen treatment Shows:Add Litter>Decrease Litter>Normal Litter.?6?The results of this study show that nitrogen deposition has different effects on the components of soil respiration.Future studies should focus more on the refinement of the research content to better explain the mechanism and provide detailed support for the study of carbon dynamics in temperate forests.