Mechanistic insights into the effects of N fertilizer application on N2O-emission pathways in acidic soil of a tea plantation

Background and aims Long-term nitrogen (N) fertilization has been shown to stimulate N 2 O emissions from acidic soil in tea plantations. However, the potential mechanism behind this stimulation remains unclear. We aimed to investigate the effects of 6 years of fertilizer application on N 2 O emission pathways and the N 2 O emission ratio from heterotrophic and autotrophic nitrification in tea plantation. Methods We performed a 15 N-tracing experiment under 40 and 60 % water-holding capacity (WHC) to investigate the effects of 6 years of fertilizer application on N 2 O-emission pathways and emission ratios from heterotrophic and autotrophic nitrification in soil from tea plantations. Results Six years of fertilizer application stimulated both heterotrophic and autotrophic nitrification, particularly under conditions of higher soil moisture. Autotrophic nitrification was the predominant pathway for N 2 O emission in tea soils, being responsible for 66.7–75.9 % and 50.4–56.9 % of N 2 O emission in unfertilized and fertilized soils, respectively. Fertilizer application significantly increased the contribution of denitrification to N 2 O emission (10.5–35.7 %), independent of soil moisture conditions, which could be due to a fertilizer-induced reduction in soil pH Fertilizer application and a subsequent reduction in pH resulted in a 3–4 and 8–9 fold increase in the ratio of N 2 O emissions from heterotrophic nitrification and autotrophic nitrification, respectively. Conclusions The increase in N 2 O emission following N fertilizer application was attributed to increased heterotrophic and autotrophic nitrification rates and an increased ratio of N 2 O emission from heterotrophic and autotrophic nitrification. Our results suggest that pH was a critical factor regulating the ratio of N 2 O emission from heterotrophic and autotrophic nitrification and thus controlling N 2 O emission from the tea soils studied.