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

Abstract

Long-term nitrogen (N) fertilization has been shown to stimulate N2O 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 N2O emission pathways and the N2O emission ratio from heterotrophic and autotrophic nitrification in tea plantation. We performed a 15N-tracing experiment under 40 and 60 % water-holding capacity (WHC) to investigate the effects of 6 years of fertilizer application on N2O-emission pathways and emission ratios from heterotrophic and autotrophic nitrification in soil from tea plantations. 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 N2O emission in tea soils, being responsible for 66.7–75.9 % and 50.4–56.9 % of N2O emission in unfertilized and fertilized soils, respectively. Fertilizer application significantly increased the contribution of denitrification to N2O 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 N2O emissions from heterotrophic nitrification and autotrophic nitrification, respectively. The increase in N2O emission following N fertilizer application was attributed to increased heterotrophic and autotrophic nitrification rates and an increased ratio of N2O emission from heterotrophic and autotrophic nitrification. Our results suggest that pH was a critical factor regulating the ratio of N2O emission from heterotrophic and autotrophic nitrification and thus controlling N2O emission from the tea soils studied.