Effects of warming and nitrogen deposition on CH4, CO2 and N2O emissions in alpine grassland ecosystems of the Qinghai-Tibetan Plateau

Abstract

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 N₂O) 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 (NH₄NO₃) (8kgNha^-1year^-1), a warming treatment using an open top chamber (OTC) was carried out, and a combined treatment of warming and N deposition (8kgNha^-1year^-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 N₂O 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.

Keywords: Alpine grasslands; Climate warming; Greenhouse gases fluxes; Nitrogen deposition; Qinghai-Tibetan plateau.