Effects of warming and fertilization on paddy N2O emissions and ammonia volatilization

Several studies have proved the influence of warming to N2O emissions and NH3 volatilization in paddies. However, it is not clear whether the performance is affected by fertilization. Here, we performed a field trial to evaluate the impacts of warming and fertilization on N2O emissions and NH3 volatilization from paddies. A free air temperature increase system was used for the experimental warming treatment (ET), while the control treatment used ambient temperature (AC). Both ET and AC treatments were combined with nitrogen (N) fertilizer (CF) or without fertilizer input (CK). The results showed insignificant interaction effects of warming and fertilization on seasonal cumulative N2O emissions and NH3 volatilization. Compared with AC, seasonal cumulative N2O emissions and ammonia volatilization in the ET treatment increased by 118.44% and 38.41%, respectively. Moreover, fertilization surprisingly stimulated seasonal cumulative N2O emissions and ammonia volatilization; values were 15.91 and 2.35 times higher than those in the CK treatment. These results imply that fertilization could intensify the increasing effect of warming on N2O emissions and ammonia volatilization. The variable importance for the projection (VIP) analysis revealed that soil N transformation (the rates of N mineralization, nitrification, and denitrification) was the key to affecting reactive N loss rather than soil fertility. Additionally, the ammonia volatilization rate increased with ambient temperature and NH4+-N solution concentration in the microsystem. Importantly, there was a "surge" inflection point of the ammonia volatilization rate under both high ambient temperature (30 degrees C) and NH4+-N concentration (15 mg/L) conditions. Our findings indicate that warming did promote N2O emissions and ammonia volatilization in paddies by accelerating soil N transformation, which might be aggravated by fertilization. Furthermore, the "surge" effect of high ambient temperature and NH4+-N concentration on ammonia volatilization deserves further attention.