Response Dynamics And Mechanism Ofsoil Carbon And Nitrogen To Nitrogen Enrichment In Loess Plateau

Nitrogen deposition has become one of the hotspots of global climate change,and it has already had an important impact on forest ecosystems.Evaluating and predicting the effects of nitrogen deposition on soil carbon and nitrogen cycling processes in forest ecosystems is important for analyzing changes in soil carbon and nitrogen and their storage in the context of global climate change.In order to better understand the response of soil carbon and nitrogen and its storage to nitrogen enrichment,this study used Pinus tabulaeformis forest as the research objection,and set the four nitrogen addition levels were control(0 kg N ha yr^-1,N0),low nitrogen(50 kg N ha yr^-1,N50),and medium nitrogen(100 kg N ha yr^-1,N100)and high nitrogen(200 kg N ha yr^-1,N200)in 2015-2017,researching the changes of carbon and nitrogen contents and storage of forest soil-litter-fine roots,discussing the main factors affecting soil carbon and nitrogen and their storage.To provide scientific basis for the scientific evaluation of nitrogen enrichment for the carbon and nitrogen cycle of forests in the region,and to provide a scientific basis for predicting the trend of carbon and nitrogen in forest soils and formulating forest utilization policies.The main research progress is as follows:?1?Nitrogen enrichment increases soil carbon and nitrogen content and storage.Soil microbial carbon and soil dissolved carbon are more sensitive to short-term nitrogen enrichment than other carbon and nitrogen componentsShort-term nitrogen enrichment affects soil carbon and nitrogen and its storage by changing different carbon and nitrogen components in the soil.The length of nitrogen enrichment is one of the main factors affecting soil carbon and nitrogen and its storage;In the first year,soil total nitrogen was significantly higher than the control level under low nitrogen and high nitrogen levels in the surface and middle soil,while nitrogen enrichment was no significant difference between the treatment and the control in the second year,and the nitrogen enrichment treatment for two years,the nitrogen treatment in the upper,middle and lower soil layers were significantly lower than other treatment levels;In the first year of nitrogen enrichment treatment,soil nitrogen storage at high nitrogen levels was significantly higher than that at control,low nitrogen and medium nitrogen levels,while only the surface soil carbon storage the middle nitrogen and high nitrogen levels was significantly higher than the low nitrogen and and control levels in the second year of nitrogen enrichment treatment;changes in soil microbial carbon and soil dissolved carbon are more sensitive to short-term nitrogen enrichment than other components.?2?Nitrogen enrichment can increase soil carbon and nitrogen and its storage by increasing litter nitrogen contentThe amount of litter under nitrogen enrichment treatment was significantly higher than the control level under nitrogen enrichment,In the first year of nitrogen enrichment,litter nitrogen was significantly higher than the control level under nitrogen enrichment treatment,while in the second year,litter nitrogen was significantly higher than the control level at low nitrogen and high nitrogen levels,and the carbon and nitrogen ratio of litter at the control level was significant higher than the level of nitrogen enrichment treatment;Redundancy analysis and principal component analysis showed that the nitrogen content of litter was the main factor affecting soil carbon and nitrogen and its storage under short-term nitrogen enrichment treatment,but its effect on soil carbon and nitrogen was lower than that fine root nitrogen.?3?Nitrogen enrichment increases soil carbon and nitrogen and its storage main by changing fine root nitrogen contentThe fine root biomass of topsoil was significantly higher than the control level under high nitrogen and low nitrogen levels in the first year;Fine root carbon was significantly higher than the control level under nitrogen enrichment treatment,and nitrogen enrichment treatment reduced fine root carbon and nitrogen ratio;In the second year,low nitrogen treatment increased the fine root biomass of the topsoil,but reduced the soil fine carbon and nitrogen ratio.Nitrogen enrichment reduced the fine root carbon content but increased the fine root nitrogen content of the lower soil;The results of redundancy analysis and principal component analysis showed that fine nitrogen was the main factor affecting soil carbon and nitrogen and its storage under short-term nitrogen enrichment treatment.