Response Of Soil Respiration And Its Components To Nitrogen And Phosphorus Addition In Farming-withdraw Grasslands At The Semiarid Loess Hilly-gully Region

Soil respiration is an important component of the carbon cycle of terrestrial ecosystems and has an important impact on global climate change.Appropriate addition of nitrogen and phosphorus will not only affect soil respiration,but also help to improve the ecological environment in loess hilly-gully region.A field experiment was performed with the farming-withdrawn grassland ecosystem dominated by Stipa bungeana and Lespedeza davurica,the field split-plot experiment is used,there are 8 treatments:single nitrogen addition(50 and 100 kg N hm^-2a^-1),single phosphorus addition(40 and 80 kg P₂O₅hm^-2 a^-1),and nitrogen with phosphorus combined addition.Research the diurnal and seasonal changes of soil respiration and its components in the farming-withdrawn grassland,and then discuss the response of soil respiration and its components to different nitrogen and phosphorus additions,and provide a reference for grassland carbon emissions and carbon cycle improvement.The main results are as follows:?1?Soil respiration and its components have obvious daily dynamic characteristics,and all show a single peak curve.The daily changes of soil temperature and soil water content are 17.4?35.9?and 3.4%?9.1%,respectively;the daily changes of soil respiration,heterotrophic respiration and autotrophic respiration are 0.42?1.36,0.26?0.74 and0.05?0.65 g m^-2 h^-1,respectively.The maximum value of soil respiration and its components in July appeared in N100P40 treatment,while the maximum value of soil respiration in August occurred in N50P80 treatment,and the maximum value of heterotrophic respiration and autotrophic respiration appeared in N100P80 treatment.?2?The soil respiration and its components have obvious seasonal dynamic trends characteristics,the maximum in summer and the minimum in winter.The average soil respiration rate,heterotrophic respiration rate and autotrophic respiration rate in the growing season were:0.60,0.35 and 0.24 g m^-2 h^-1,respectively.The average soil respiration rate,heterotrophic respiration rate and autotrophic respiration rate in the non-growing season were:0.13,0.06 and 0.07 g m^-2 h^-1,respectively.The addition of nitrogen and phosphorus will significantly increase the soil respiration and its components in the growing season,but has no effect on the soil respiration and its components in the non-growing season.Nitrogen or phosphorus addition will improve soil respiration and its components,but the combined effect of nitrogen and phosphorus addition is better.Soil respiration and autotrophic respiration were the largest in N100P80 treatment,while heterotrophic respiration was the largest in N50P40 treatment.It shows that the effects of different concentrations of nitrogen and phosphorus additions on soil respiration and its components are not only related to the amount of nitrogen and phosphorus addition,but also affected by different components of soil respiration.?3?Nitrogen and phosphorus addition mainly affects soil autotrophic respiration and heterotrophic respiration by affecting plant biomass,soil nutrients,root nutrients and microbial biomass.Autotrophic respiration has a significant positive correlation with plant aboveground biomass,underground biomass and root nitrogen content.Nitrogen and phosphorus addition promotes autotrophic respiration by increasing plant aboveground biomass,underground biomass and root nitrogen content.Heterotrophic respiration has a significant positive correlation with microbial biomass carbon and soil total phosphorus.Nitrogen and phosphorus addition improves heterotrophic respiration by increasing microbial biomass carbon and soil total phosphorus.