Responses of Soil Nitrous Oxide Emission to Nitrogen Addition at Two Topographic Positions of a Subtropical Forest

Abstract

Topography can influence nitrous oxide (N2O) emission via its influences on soil nutrient availability, moisture, and microbial communities. Nevertheless, it is still unclear whether topography modulates the responses of soil N2O emissions to elevated N deposition. Here the N addition experiment was conducted in the valley and on the slope of a subtropical karst forest in southwest China. Nitrogen was applied as NH4NO3 in two levels, that is, 50 (moderate N) and 100 (high N) kg N ha−1 yr−1 with no N addition plots as the control. Nitrogen addition consistently increased N2O emission in the valley, but only high N addition significantly increased N2O emission on the slope in 2017. The cumulative N2O fluxes across the 3 years were 1.16 ± 0.24 kg N ha−1 in the valley and 1.50 ± 0.06 kg N ha−1 on the slope under the control. Nitrogen addition stimulated N2O emission by 88.7%–113.3% in the valley due to increased ammonium, nitrate and dissolved organic carbon availabilities and ammonia‐oxidizing bacteria (AOB) amoA abundance. High N addition stimulated N2O emission by 84.3% on the slope owing to increased nitrate and carbon availabilities, AOB amoA, and nirK abundances. The stimulation of N2O emission by moderate N addition was more pronounced in the valley than on the slope largely owing to the lower N status in the valley. This work highlights the importance of N status in regulating the responses of soil N2O emissions to elevated N deposition.