Effects of optimized nitrogen application on CH4 emissions from flooded paddy fields under elevated atmospheric CO2 concentrations
The aim of this study was to explore the rational management of nitrogen fertilizer under future climate change condition,achieve low-carbon emissions,and maintain rice yield.The effects and mechanisms of elevated atmospheric CO2 concentration(120 μmol·mol-1)and reduced nitrogen application rate(40%)on rice production and CH4 emissions in flooded paddy fields were investigated in this study.Four treatments were set up using open-top chambers(OTCs)to automatically control the CO2 concentration:ambient CO2 concentration+nitrogen application by 250 kg·hm-2(CK),elevated atmospheric CO2 concentration by 120 μmol·mol-1+nitrogen application by 250 kg·hm-2(C+),ambient CO2concentration+nitrogen application by 150 kg·hm-2(N-),elevated atmospheric CO2 concentration by 120 μmol·mol-1+nitrogen application by 150 kg·hm-2(C+N-).The cumulative amount of CH4 emissions(CAC),rice biomass and yield,soil physicochemical properties,and enzyme activities were analyzed.The results showed that compared with CK treatment,the C+treatment significantly increased CAC/yield by 16.93%,N-treatment significantly decreased CAC/yield by 13.33%,and C+N-treatment decreased CAC/yield by 7.89%,but this was not significantly.N-treatment weakened the promoting effect of C+on CAC,CAC/yield,rice biomass,and soil-soluble organic carbon concentration to a certain extent.Stepwise regression analysis showed that the linear model based on dissolved organic carbon and nitrate nitrogen content and soil urease activity could explain 64%of the variation in cumulative CH4 emissions from paddy fields.In summary,nitrogen fertilizer reduction can regulate CH4 emissions from paddy fields under elevated atmospheric CO2 concentrations by affecting soil carbon,nitrogen substrates,and urease activity.
elevated atmospheric CO2 concentrationnitrogen fertilizer reductionCH4 emissionsrice production