N2O emissions from N saturated subtropical forest in South China

Surplus of reactive nitrogen (Nr) is one of China's most pressing environmental problems, and may cause a positive feedback to climate change through increased N2O emission. We previously found that forests in sub-tropical China receiving high atmogenic N loads (> 4g N m-2 yr-1) differ in their apparent ability to retain Nr, suggesting that denitrification may be a major sink for excess N and that forests may become N-saturated. Rapid N-cycling and the monsoonal climate with wet, warm summers imply potent ially high N2O emissions from multiple sources but no systematic assessment of N2O emissions on a watershed level has been conducted yet. We therefore propose a multidisciplinary study in an N-saturated research site (TieShanPing, Chongqing, PR China) aim ing at identification of hotspots for nitrification, denitrification and N2O emissions in relation to the availability of Nr and hydrological conditions. The overall goal is to estimate N2O emission rates in humid sub-tropical south China and to understan d the environmental controls at a watershed level. Ultimately, these data are needed to facilitate upscaling approaches for N2O emissions and to predict the effect of changing hydrological conditions on N2O emissions at a regional scale. Our approach draw s on a strong alliance of Sino-Norwegian expertise in terrestrial biogeochemistry proven in previous projects. The proposed project provides an important arena for Sino-Norwegian exchange of expertise with respect to quantification and process understandi ng of greenhouse gas emissions from forest and mountain ecosystems.