Carbon isotopic signature reveals the geographical trend in methane consumption and production pathways in alpine ecosystems over the Qinghai-Tibetan Plateau

On the Qinghai-Tibetan Plateau, isotopic signatures in soil-atmosphere CH4 fluxes were investigated in nine grasslands and three wetlands. In the grasslands, the fractionation factor for soil CH4 uptake, a(soil), was much smaller than the usually reported value of 0.9975-1.0095. Stepwise multiple variation analysis indicates that asoil is higher for higher soil water contents but is lower for higher C/N ratios of soil surface biomass. In the three wetlands, the soil-emitted delta C-13-CH4 was similar (-55.3 +/- 5.5% and -53.0 +/- 5.5%) in two bogs separated by > 1000 km but was lower (-63.4 +/- 6.3%) in a marsh. Environmental factors related to intrasite variations in soil-emitted delta C-13-CH4 include the soil C/N ratio, oxidation-reduction potential, soil C concentration and soil water contents. Geographical isotopic surveys revealed environmental constraints on the CH4 consumption pathways in grasslands and the biome type-specific consistency in CH4 production pathways in wetlands.