Effects of nitrogen deposition on N2O emission in a wet meadow on the Qinghai-Tibet Plateau

Northwest China wet meadows with large organic carbon storage have the potential to be N2O hot spots under elevated nitrogen (N) deposition due to climate change. However, the main controlling factors of N2O fluxes in wet meadows at different N deposition levels are not well-known. Here, we conducted a wet meadow experiment simulating different amounts of N deposition to study N inputs induced changes in N2O flux and the underlying abiotic and biotic mechanisms. We found that the amount of N deposition significantly affected the N2O flux. The N2O flux increased first and then decreased with the increase of N deposition, and the high concentration of N addition (15 g center dot m (-2)center dot a (-1)) limited the N2O emission, mainly because the high nitrogen content changes the nutrient limiting (nitrogen confinement is transformed into phosphorus confinement) factors in Qinghai-Tibet Plateau area, resulting in the lack of substrate (soil available phosphorus) for N2O production. The N deposition effect on N2O emissions was related to the amount of N input and date of measurement, which was mainly attributed to changes in soil properties (soil available nutrients, non-capillary porosity and aeration) after nitrogen input. Furthermore, vegetation biomass was found to be a key controlling factor for N2O fluxes under N addition conditions. Our results emphasize that the interaction of abiotic (soil nutrients, water content and temperature) and biotic factors (microbial community structure changes) on N2O fluxes should be taken into account in order to accurately project N2O fluxes in wetland ecosystems.