Effects of warming and nitrogen deposition on CH 4 , CO 2 and N 2 O emissions in alpine grassland ecosystems of the Qinghai-Tibetan Plateau.

Increases in nitrogen (N) deposition along with climate warming can change the dynamics of carbon and nitrogen in the soil, and alter greenhouse gases (GHGs) fluxes. To examine how N deposition and warming affect GHGs (CH4 , CO2 and N2 O) fluxes in alpine grasslands, we conducted experiments in an alpine meadow (AM), alpine-steppe (AS), and alpine cultivated grassland (CG) on the Qinghai-Tibetan Plateau (QTP). We simulated N deposition by treating soil with ammonium nitrate (NH4 NO3 ) (8kgNha-1 year-1 ), a warming treatment using an open top chamber (OTC) was carried out, and a combined treatment of warming and N deposition (8kgNha-1 year-1 ) was conducted. The GHGs were collected during early, peak, and late plant growing seasons, i.e., May, August, and October of 2015, respectively, using a static chamber. We found, in general, neither N deposition nor warming solely altered CH4 and N2 O fluxes in the alpine grasslands. The N deposition under warming conditions reduced CO2 emission significantly. The reduction of CO2 emission was most significant in the alpine steppe. The effects of climatic warming and N deposition on the GHGs varied greatly across the grassland types and the growing seasons. The cultivated grasslands were much more unstable than the native grasslands in CH4 uptake. In can be concluded the N deposition associated with human activities may buffer the CO2 emission in the alpine grassland ecosystems in terms of climate changes on the QTP.