Simulated warming and low O2 promote N2O and N2 emissions in subtropical montane forest soil

Purpose The montane subtropical forest soils contain huge nitrogen stocks, and climate warming might drive its volatilization due to the promotion of gaseous losses of nitrous oxide (N2O) and dinitrogen (N-2), contributing a positive feedback to promote further warming. However, it is unclear how temperature increase in subtropical forests affects the loss of gaseous N and the mediated microbial mechanisms. Methods In this study, we employed the acetylene inhibition technique and molecular method to quantify N2O and N-2 emissions as well as its microbial pathways under simulated warming and oxygen (O-2) conditions in a subtropical forest (> 300 years old) soil. Results During the aerobic incubation, short-term increase of temperature of 2 celcius caused an increase in N2O emission by a factor of 4.8, while under anaerobic conditions, N2O and N-2 emissions increased 18- and 1.9-fold, respectively, thus leading to a significant increase of the ratio of N2O/(N2O + N-2). Structural equation modeling showed that the increased potential of N2O loss under simulated warming could be explained by the reduction of nosZ-I gene abundance and thus the less N2O reduction to N-2, as well as the promotion on SOC mineralization by the temperature increase, which provides more substrate DOC and nitrate for denitrification. Conclusion These findings suggest the nitrate substrate concentration and availability, together with the abundance variation of denitrifiers to produce and emit N2O, resulted the consequence of the increased N2O in response to the temperature increasing. Results contribute to the accurately establish models of N2O and N-2 emissions in the subtropical montane forest soils and the budgets of global greenhouse gas.