Study On The Effect Of Stimulated N Deposition On N₂O Emission And Fate Of Nitrogen In A Stipa Krylovii Steppe

With fast development of industry,agriculture and society,China became the highest N deposition zone in the world.N deposition had exceeded 3g�m^-2�a^-1 in some area of temperate steppe,which may have influence on the N cycling of the grassland ecosystem.Except for the influence of the plant biomass or production,biodiversity,physical and chemical properties of soil within this area,N deposition may also increase the N₂O emission in the temperate grassland.N₂O as the main greenhouse gas,its emission flux and characteristics in the temperate grassland need to be measured,to know well about the N cycling characteristics and effects,which may offer the scientific evidence to the policy setting of air pollution control and climate change.From 2014 to 2016,a field control experiment of simulated N deposition(by NaNO₃ addition,0-50 g�m^-2�a¹,6 does treatment)and ¹⁵N isotope tracer experiment were carried out in a Stipa krylovii steppe in Inner Mongolia.With the Chamber+GC method,N₂O flux under different N addition treatments were measured for two whole years.N content and ¹⁵N isotope abundant(?¹⁵N)of soil,plant and N₂O were measured to study the fate of N in different N pool or gases sink and N₂O emission mechanism.The results under the simulated N deposition experiment showed that,under ambient N deposition,summer was the mean N₂O emission season,and the observed flux in freezing-thawing period was little.N₂O flux depended on the soil temperature and soil moisture?WFPS?,and the estimated annual N₂O emission was 0.04g�m^-2�a^-1?according to the N,see below?,accounting for about 1%of the total N deposition.In addition,enhanced N deposition might increase N₂O emission,but only increased significantly under 50 g�m^-2�a^-1 treatment.The results under ¹⁵N isotope tracer measurement showed that,in the short term,?within the whole growing season?,the N input was mainly retained in the soil pool and plant pool.Above the 5 g�m^-2�a^-1 N addition,soil exchangeable NO₃^-increased rapidly,showed the N saturation.According to the response of ¹⁵N₂O emission to the ¹⁵NO₃^-addition and the relationship between N₂O emission and soil exchangeable NH₄⁺in freezing-thawing period,nitrification might be the main process to the N₂O emission.Ammonium deposition might have significant effect on the N₂O emission in the soil.