Soil microbial abundance and diversity: CK-2
The application of nitrogen (N) fertilizer can promote rice yield, but is accompanied by considerable quantities of ammonia (NH3) volatilization and greenhouse gases (GHGs) emission, and the response to N-fertilizers under saline-alkali condition is not yet clear. A 137-day experiment was carried out to clarify the effect of different N-fertilizer application strategies on NH3 volatilization and GHGs emission in saline-alkali paddy ecosystems and to determine the microbiological mechanisms. Five N-fertilizer treatments consisting of control without additional N-fertilizer (CK), urea (U), urea with urease-nitrification inhibitors (UI), organic-inorganic compound fertilizer (OCF) and carbon-based slow-release fertilizer (CSF) were established. By the end of the rice-growing season, the cumulative NH3 emissions of CSF and UI treatments were higher than U and OCF, respectively. For GHGs, the cumulative methane (CH4) emissions in all N-fertilizer treatments were decreased compared with CK. The cumulative carbon dioxide (CO2) emissions were U > CSF > OCF > CK > UI, and the order for nitrous oxide (N2O) was U > CSF > UI > CK > OCF. For the global warming potential (GWP), the value in UI was lower than all the other treatments. Compared with the other N-fertilizer treatments, the relative abundances of N-related functional bacteria (genus Sphingomonas and class Alphaproteobacteria) in OCF treatment were increased, and the (nirS+nirK)/nosZ ratio was reduced, thereby decreasing the N2O emission. Overall, the U is a better choice for controlling NH3 volatilization in a saline-alkali paddy ecosystem during the entire rice-growing season. The UI and OCF are more beneficial for reducing GHGs emission.