Elevated Carbon Dioxide And Air Temperature Effects On The Emissions Of Methane And Nitrous Oxide,and Soil Microbes In A Double Rice Cropping System

Rice paddy is the main sources of man-made CH4 and N2O,and soil microbes play important role in its soil carbon and nitrogen cycling.However,the empirical relationships of microbial community composition with methane(CH4)and nitrous oxide(N2O)emissions in rice paddy under future climate are poorly understood.A field Open Top Chamber(OTC)experiment was conducted to evaluate the effects of elevated air temperature(ET),elevated CO2 concentration(EC)and simultaneously elevated air temperature and CO2 concentration(ETC)on CH4 and N2O emissions.More attention was paied to microbial community compositions(functional amoA genes of ammonium bacteria(AOB)and ammonium archaea(AOA),functional mcrA gene of Methanogenic archaea(MOA)and pmoA gene of methanotroph bacteria(MOB))and soil carbon and nitrogen contents(i.e.,dissolved organic carbon(DOC),ammonium nitrogen(AMN),nitrate nitrogen(NIN)during the different growing stages(i.e.,days after transplanting(DAT))of a double rice cropping system.The purpose of this study was to reveal major factors that regulating rice paddy CH4 and N2O emissions under climate,to provide scientific basis for the mechanisms of soil microbes and soil carbon and nitrogen availability that involved in rice paddy carbon and nitrogen cycling.Compared to ambient conditions,EC,ET and ETC significantly enhanced total annual CH4 emissions,increased 25.56%,36.98%and 53.95%,respectively.EC,ET and ETC effects on annual N2O emissions were not significant.Treatment effects on seasonal and annual total CH4 and N2O emissions were different.Growing stages significantly influenced rice paddy CH4 and N2O emission rates.Compared to CK,the increasing and decreasing effects of EC,ET and ETC on rice paddy CH4 and N2O emission rates differed among different growing stages.The interactive effects of ET and EC significantly influenced CH4 emission rates but not N2O emission rates in the two growing seasons.Based on the method of Hedge's d,interactive effects of ET and EC were additive in both seasonal and annual rice CH4 and N2O emission.Growing stages significantly influenced DOC,AMN and NIN.ET,EC and their interactive effects on soil AMN and NIN were all not significant.Only EC significantly influenced DOC in both early and late rice.ET,EC,growing stages and their interactive effects on the relative abundances of methanogen(mcrA gene),methanotroph(pmoA gene),ammonium bacteria and archaea(amoA genes)T-RFs were different among different T-RFLPs.RDA results showed that growing seasons had more influences on the relative abundance of T-RFLPs of the four microbes(i.e.,AOA,AOB,MOA and MOB)than that of treatments on them.DOC,rather than AMN and NIN,were significantly positive correlated with early rice total CH4 emissions and late rice total N2O emissions.This indicated that under elevated air temperature and air CO2 concentarions,rice paddy soil DOC availability was more important than nitrogen availability in our study.Stepwise linear regression analysis showed,when only considered growing seasons,NIN and AMN were selected as the best predictors in predicting early and late rice paddy CH4 emission rates,respectively.NIN was selected as the best indicators in predicting early and late rice paddy N2O emission rates.When only considered treatments,or considered both growing seasons and treatments,the best predictors of rice paddy CH4 and N2O emission rates were depends on treatments and growing seasons.More deep research is recommended to understand the functions and members of microbial community contribute to soil CH4 and N2O flux to further understand microbes involves in soil carbon and nitrogen cycles under future climate warming.