Effects Of Nitrogen Deposition And Alterations Of Litter Input On Soil Respiration In Horqin Sandy Grassland

The aggravation of human activity has led to the increase of nitrogen deposition year by year,and this phenomenon will continue in future.The increase of nitrogen deposition affects the primary productivity of terrestrial ecosystem profoundly,which eventually changes the input of litter to soil.The effects of nitrogen deposition and litter input on soil respiration were studied under the background of the increasingly serious problem of nitrogen deposition,which endows important scientific significance to predict the response trend of soil carbon cycle in sandy grassland under the background of global change in the future.This study was conducted in Horqin sandy grassland relied on the Naiman Desertification Research Station,Chinese Academy of Sciences.Control experiment was carried out by setting up nitrogen deposition(N0,N10)and changing the litter input(control,litter doubling,litter removal and burning),then we dynamically monitored the rate of soil respiration,root respiration and microbial respiration during the whole plant growing season,and determined soil microbial biomass carbon and nitrogen content.Moreover,the responses of soil respiration components to nitrogen deposition and litter input were discussed,and the main effects of nitrogen deposition and litter input on carbon cycling were revealed in sandy grassland ecosystem.It is aim to deepen the comprehensive understanding of the carbon cycle process,and to provide theoretical support for the scientific evaluation of the carbon cycle in semi-arid sandy grassland in the northern China.The main findings of the study are as follows:(1)The rate of soil respiration,microbial respiration and root respiration in Horqin sandy grassland showed obvious seasonal dynamic changes during the whole growing season.Respiration was lowest in late June,and reached the highest in the peak season of plant growth(late July to early August).Nitrogen deposition and changes of litter input had no significant effect on the seasonal dynamics of root respiration,microbial respiration and soil respiration in sandy grassland.(2)Nitrogen deposition had a significant effect on soil respiration rate of sandy grassland in growing season(p < 0.01).The soil respiration rate of the control treatment varied from 1.10 ?mol CO2·m-2·s-1 to 3.92 ?mol CO2·m-2·s-1 during the whole growing season.The Soil respiration rate of Nitrogen addition treatment fluctuated between 0.92 and 4.69 ?mol CO2·m-2·s-1,and nitrogen adding increased the average soil respiration rate of sandy grassland by 14%(p < 0.01).nitrogen addition increased the root respiration rate of community by 27%(p < 0.05)averagely,but it had no significant affect on microbial respiration(p > 0.05).Therefore,the significant promotion of soil respiration rate in sandy grassland was mainly due to the contribution of root respiration.(3)Changing litter input had significant effect on soil respiration(p < 0.05).Compared with the control treatment,soil respiration was decreased by 15% after litter removal,which is mainly due to removal of litter significantly inhibited soil microbial respiration(p < 0.05),but had no significant effect on root respiration incommunity.Burning decreased the microbial respiration rate by 13%(p < 0.05),but the root respiration rate increased by 25%(p > 0.05),as a result,the effect on soil respiration was not obvious.In addition,the adding of litter input had no significant effect on soil respiration,microbial respiration and root respiration(p > 0.05).(4)Nitrogen addition had no significant effect on soil microbial biomass carbon content(p > 0.05),litter doubling increased soil microbial biomass carbon content by21%(p < 0.05),burning and litter removal decreased soil microbial biomass carbon content by 25% and 25%,respectively(p < 0.05).Soil respiration rate and microbial respiration rate were positively correlated with soil microbial biomass carbon content(p < 0.05),but root respiration rate had no significant correlation with soil microbial biomass carbon content(p > 0.05).In conclusion,nitrogen addition had significant effect on soil respiration in sandy grassland in Horqin sandy grassland,and which was mainly due to the contribution of root respiration.The removal of litter reduced the substrate supply of soil respiration,which led to decrease microbial biomass and microbial respiration significantly,while adding litter input significantly increased soil microbial biomass.However,increasing litter input had no significant effect on soil respiration.Burning inhibited microbial respiration and increased root respiration rate,as a result,it had not significant effect on soil respiration.The results of the study are of great significance for further understanding of soil carbon cycle and the scientific evaluation of the carbon balance of the grassland ecosystem in the context of global change.