Study Of Short-term Nitrogen Addition On Greenhouse Gases Emissions And Its Impact Factors In Semiarid Grassland

The rapidly increase of atmosphere nitrogen(N)deposition,due to the overused of N fertilizer,industrialization and fossil fuel combustion,had a directly effects on the structure and function of terrestrial ecosystems of global world.Grassland ecosystem,as one of the most important terrestrial ecosystems,played an important role in regulating global climate change.In order to explore the response mechanism of N deposition on semiarid grassland ecosystem,we conducted a situ experience about different N addition levels in a semiarid grassland in agro-pasture ecotone of the northern Shanxi,this study used randomized block design,and made eight N addition levels,included 0?1?2?4?8?16?24 and 32 gNm-2 y-1,respectively.And we measured the greenhouse gases emission fluxes using static chamber-meteorological chromatography method,and researched the effects of N deposition to vegetation productivity,soil nutrient and greenhouse gases emission fluxes in semiarid grassland ecosystem.The results showed that:1 N addition levels had different effects on greenhouse gases in semiarid grassland.In the growing season,CO2 emission fluxes had obvious seasonal dynamics,there was a peak value in June.And we found that low N addition levels promoted the CO2 emission,however,high N addition levels inhibited the CO2 emission,the CO2 emission fluxes under the treatments of N24 reached maximum,which was significant higher than other treatments(P<0.05).And there were a significant curve correlation between N addition levels and CO2 emission fluxes(P<0.05).In addition,CH4 and N2O emission fluxes had no obvious seasonal dynamics in the whole growing season in semiarid grassland,but which had significant difference between the different N addition levels(P<0.05).N addition levels had significant curve correlation relationship with annual mean CH4 emission fluxes(P<0.05),but which had no significant correlation with annual mean N2O emission fluxes(P>0.05).The results of repeated measures ANOVAs testing showed that N addition levels and sampling dates had extremely significant effect on three greenhouse gases(P<0.001),but the interaction of them had no effects on CO2 and CH4 emission fluxes(P>0.05),but which had extremely significant effects on N2O emission fluxes(P<0.001).2 The CH4 fluxes was inhibited significantly with the increasing of aboveground biomass(P<0.05),but there were no significant correlations between aboveground biomass and CO2 and N2O emission fluxes(P>0.05).Net belowground productivity had significant correlation with CO2 emission fluxes(P<0.05),but which had no significant correlation with CH4 and N2O fluxes(P>0.05).3 There were significant negative relationship between soil pH and CH4 fluxes(P<0.05),however,soil pH had no correlations with CO2 and N2O emission fluxes(P>0.05).Soil organic carbon had significant positive correlation with CO2 emission fluxes(P<0.05),but which had no significant relationship with CH4 and N2O fluxes(P>0.05).And soil total nitrogen had no obvious correlation with greenhouse gases fluxes(CO2,CH4 and N2O)(P>0.05).4 Soil microbial carbon had significantly positive correlation with CO2 emission fluxes in semiarid grassland(P<0.05),but which had no significant correlation with CH4 and N2O fluxes(P>0.05).In addition,there were no significant relationship between soil inorganic nitrogen and greenhouse gases(CO2,CH4andN2O)(P>0.05).5 Air temperature and soil temperature had significantly positive correlation with CO2 emission fluxes in semiarid grassland(P<0.0001),but which had no significant relationship with CH4 and N2O fluxes(P>0.05).There were no significant relationship between soil moisture and CO2 and CH4 fluxes(P>0.05),but soil moisture had significantly negative correlation with N2O fluxes(P<0.0001).