Spatial variability of CH4 and N2O fluxes in alpine ecosystems on the Qinghai–Tibetan Plateau

Abstract

Abstract The intra- and inter-site spatial variability of methane (CH 4 ) and nitrous oxide (N 2 O) fluxes were investigated in three alpine ecosystems at Haibei station on the Qinghai–Tibetan Plateau (QTP) in summer 2005 and in sixteen alpine ecosystems with various vegetations across the QTP in summer 2006, respectively. The magnitude of average CH 4 emissions from wetlands was at least 100 times larger than average CH 4 uptake by grassland, suggesting that the entire QTP is likely to be a source of methane in summertime because of a significant fractional area of wetlands (∼ 2.2%) on the plateau. Intra-site investigation, with sixteen chambers, revealed a significant negative relationship of CH 4 emissions with the C/N ratio of aboveground biomass and soil pH in the alpine wetland when all chambers were considered. Moreover, soil oxidation–reduction potential (ORP) had a remarkably strong influence on CH 4 emissions for nine chambers above the water level, resulting in a negative exponential relationship. For N 2 O flux in alpine meadows, a negative relationship with both soil pH and livestock dung biomass was observed. Aboveground plant biomass and soil pH were important variables overall in wetlands. Inter-site investigation found positive and negative relationships between CH 4 flux and soil biomass to 5 cm depth in nine grassland and seven wetland sites, respectively. N 2 O flux showed a moderately strong negative exponential relationship with the C/N ratio of surface soil in the grassland sites. In the wetlands, soil pH was negatively correlated with N 2 O flux, perhaps due to both reduced N 2 O release from suppressed nitrification and denitrification.