Multivariate regression analysis of greenhouse gas emissions associated with activities and populations of soil microbes in a double-rice paddy soil Effects of exogenous nitrogen input on the CH4 and N2O fluxes in freshwater marshes Effect of different application time of DCD on methane and nitrous oxide emissions during rice growth period The effect of soil oxygen availability on greenhouse gases emission in a double rice field Emissions of CO2, CH4 and N2O from broad-leaned forested swamp soils in Xiaoxingan Mountains