Nitrous oxide fluxes and nitrifier and denitrifier communites as affected by dry-wet cycles in long term fertilized paddy soils

Drying and rewetting events of soil represents a common physiological stress for soil microbial communities. We investigated the effect of alternate drying-rewetting cycles on N2O emissions and soil microbial communities in jar experiments with soil samples. The results showed that instant flooding and air-drying moments are two important steps of soil drying and rewetting periods influencing soil microbial communities and N2O emissions. N2O fluxes in the air dry (AD) steps were always higher than those in the instant flooding (IF) steps, especially in the early stages of AD and IF. The soil treated with long-term organic matter and chemical fertilizer promoted N2O emissions but inhibited the N2O release from newly applied urea when soil went through drying and rewetting events. Soil moisture content(s) also significantly affected the growth of ammonia oxidiser and denitrifier communities, with the functional gene abundance increasing with increasing soil moisture content. While comparing first and second cycles, N2O fluxes were six times higher in the first cycle than in the second cycle. It is concluded that sudden changes in moisture condition influenced the N2O flux, and nitrifier and denitrifier functional genes by affecting the growth of ammonia oxidiser and denitrifier communities.