Experimental Warming Increases Seasonal Methane Uptake in an Alpine Meadow on the Tibetan Plateau

Abstract

Increased understanding of the response of soil methane (CH4) uptake in alpine meadow ecosystems to warming and grazing could reduce uncertainty in estimates of the soil-atmospheric CH4 budget. To determine the effects of warming and grazing on soil CH4 uptake at different timescales (that is, daily, monthly, seasonal, and annual), we conducted a controlled warming and grazing experiment [that is, no warming with no grazing (NWNG), no warming with grazing (NWG), warming with no grazing (WNG), and warming with grazing (WG)] in an alpine meadow on the Tibetan plateau from 2006 to 2009. Soil CH4 uptake was mainly affected by warming and sample date and their interaction. Warming treatment regardless of grazing significantly increased seasonal average CH4 uptake by 31-39% during the growing season (from May to September) and by 162% during the non-growing season (from October to April next year) in 2007-2008, whereas only WNG increased seasonal average CH4 uptake by 87-138% compared with NWNG during the non-growing seasons in 2006-2007 and 2008-2009. Warming in WNG and WG increased annual CH4 uptake by 50-87% compared with NWNG or NWG. Moreover, warming regardless of grazing and warming with grazing (compared with NWNG) significantly increased the contribution to annual uptake of CH4 uptake during the non-growing season in 2007-2008 and 2008-2009. However, moderate grazing did not significantly influence soil CH4 uptake, although grazing with warming decreased CH4 uptake by 43% during the growing season in 2006. Soil moisture explained 16-25% of the CH4 variation during the growing season, but there was no significant relationship between soil CH4 uptake and soil moisture during the non-growing season. Our results suggest that more attention should be paid to the stimulating effect of warming on soil CH4 uptake during the non-growing season due to its greater response to warming and different stimulating mechanisms compared to responses during the growing season in the alpine meadow.