Variations of N2O fluxes in response to warming and cooling in an alpine meadow on the Tibetan Plateau

Little is known about the impacts of climate change especially for cooling on N2O emissions from alpine meadows on the Tibetan Plateau. Along a slope of Qilian mountains, China, we transferred intact soil cores covering different vegetation types (graminoid, shrub, forb, and sparse vegetation) downhill (warming) and uphill (cooling) across a 600-m elevation gradient to examine the responses of soil-atmosphere N2O exchange rates to climate warming and cooling. N2O fluxes were measured during two growing seasons from May to October in 2008 and 2009. The Tibetan alpine meadow acted as a net N2O source at an average rate of 5.2 mu g m(-2) h(-1) (ranging from 2.0 to 11.5 mu g m(-2) h(-1)). In situ N2O emission generally decreased with elevation increase except for sparse vegetation, but significant differences were only found between graminoid and other three vegetations in 2008 and between graminoid and shrub vegetation in 2009. Warming averagely increased mean N2O fluxes by 219% (ranging from 126 to 287%) while cooling decreased it by 75% (ranging from 57 to 95%) across four vegetation types over the variation of soil temperature from 1.3 to 5.5 A degrees C. However, opposite effects were also observed in some cases due to modification of variations in soil moisture. Soil temperature and moisture had a positive effect on N2O fluxes and explained 48 and 26% of the variation in mean N2O fluxes across the four vegetation types, respectively. No relationship was found between mean N2O fluxes and aboveground biomass. Our results suggest that more N2O-N would be released from soil in a warmer future and that less N2O emission during cool and dry years is expected in the Tibetan alpine meadow.