Effects Of Nitrogen Addition On Greenhouse Gas Flux In A Stipa Baicalensis Grassland In Inner Mongolia

Atmospheric nitrogen deposition as an important phenomenon of global climate change,it has an important influence on grassland ecological system.Research on effects of nitrogen deposition on greenhouse gas fluxes of the Stipa baicalensis grassland,provides theoretical basis of comprehensive analysis and evaluate the effects of global change of grassland ecological system,also for the reasonable use and the degraded grassland restoration.This study based on a long-term platform of Stipa baicalensis grassland original exogenous nitrogen addition nitrogen deposition field control simulation test,we set four different nitrogen addition levels?0?30?50?100 kg N hm-2a-1?in the Stipa baicalensis grassland in Inner Mongolia,to study the effects of nitrogen addition on greenhouse gas flux,soil physical and chemical properties and soil microbial community structure and the relationship between the three.The main results were as follows:1.Using the methods of static chamber-box gas chromatography to determine the fluxes of greenhouse gas under different nitrogen addition levels,the results show that:during the growing season,that the Stipa baicalensi.s grassland is a source of CO₂ and N₂O,but a sink for CH₄.The total average flux of CO₂,CH₄ and N₂O is respectively 595.68,-0.09 mg·m-2·h-1 and 17.99 ug·m-2·h-1,during the experiment.Nitrogen addition increase the above-ground biomass of the plants significantly and enhance the emissions of CO₂ and N₂O,whereas it decrease the uptake of CH₄.The global warming potential of the treatments follow the order of N100>N30>N50>CK.The global warming potential growth of N30 and N50 treatments are around 25%.Thus,N50 treatment not only significantly increase the above-ground biomass.but also reduce the increase of global warming potential.2.The study of soil inorganic nitrogen content of Stipa baicalensis grassland,and the results show that:from 0 to 40cm soil layers of the grassland,the content of soil ammonium nitrogen are higher than soil nitrate nitrogen content in CK,N30 and N50 treatment,but half and half in N100 treatment,the variation tendency of inorganic nitrogen content consistent with nitrate nitrogen in the growing season.The contents of soil ammonium nitrogen,nitrate nitrogen and inorganic nitrogen are increased within the increase of nitrogen addition,however,along with the soil layer deepen decreased.The analysis of variance showed that,nitrogen addition,sampling time,soil layer and their interactions have significant impact on the soil ammonium nitrogen,nitrate nitrogen and inorganic nitrogen content.The accumulation of nitrate nitrogenre is obviously in N100 treatment,is 6.73 times of comparison,so N100 treatment has reached the "nitrogen saturation point" in the present study;The highest total phospholipid fatty acid content of soil is 63.87 nmol·g-1 in the experiment.Nitrogen addition significantly increase the content of soil bacteria,gram-positive bacteria and gram-negative bacteria,and decrease the biomass of fungi and gungi/bacteria in soil;In N30 and N50 treatments,total phospholipid fatty acid and actinomycete content are significantly higher than control,the ratio of gram-positive bacteria/gram-negative bacteria is significantly lower than control.3.The fluxes of CO₂,CH₄ and N₂O show significant correlations with soil temperature,organic carbon and nitrate nitrogen content?p<0.05?.CO₂ and N₂O fluxes also show significantly positive correlations with soil moisture?p<0.05?.In addition,CH₄ and N₂O fluxes have significant relationships with soil ammonium nitrogen content?p<0.01?.CO₂ and N₂O fluxes show significantly positive correlations with total phospholipid fatty acid,bacteria,gram-positive bacteria and gram-negative bacteria in soil,CH₄ flux have significant negative correlation with bacteria and gungi/bacteria,N₂O fulx have significant negative correlation with gungi/bacteria also.