Nitrogen addition increases CO2, CH4, and N2O concentrations of topsoils and subsoils in a subtropical Moso bamboo forest

Forest soils play a vital role in regulating the balance between the production and consumption of global soil greenhouse gases (GHGs), such as CO2, CH4, and N2O. However, the effect of N addition on GHGs concentrations at different soil depths in subtropical forests has never been elucidated. We conducted a two-year field study to investigate the effects of different N addition rates (0, 30, 60, and 90 kg N ha(-1) year(-1), defined as Control, N30, N60, and N90) on CO2, CH4, and N2O concentrations in the topsoil (0-20 cm) and subsoil (20-40 cm) in a subtropical Moso bamboo (Phyllostachys edulis) forest. Soil CO2 and N2O concentrations increased with soil depth and showed patterns of seasonal variation, being higher in summer and lower in winter. Soil CH4 concentrations declined with soil depth and showed erratic patterns of seasonal variations. N addition significantly increased the annual topsoil concentrations of CO2 (23.2-81.5%), CH4 (28.1-93.8%), and N2O (52.1-210.9%) and the annual subsoil concentrations of CO2 (21.5-74.2%), CH4 (36.8-109.2%), and N2O (54.5-249.2%), but did not change the seasonal patterns of the three GHGs. The CO2 concentration of the topsoil was more responsive to N addition than that of the subsoil, whereas the CH4 and N2O concentrations showed the opposite response pattern. Soil CO2 concentration was significantly and positively correlated with soil temperature and volumetric water content (VWC). Soil CH4 concentration was significantly negatively correlated with soil pH. Soil N2O concentration was significantly positively correlated with soil temperature, VWC, and soil total nitrogen. These findings indicate that N addition increased CO2, CH4, and N2O concentrations at different soil depths in Moso bamboo forests. These results contribute to a better understanding of GHG fluxes from forest ecosystem, and their responses to the increasing atmospheric N deposition.