Winter soil CO2 efflux in two contrasting forest ecosystems on the eastern Tibetan Plateau, China

Significant CO2fluxes from snow-covered soils occur in cold biomes. However, little is known about winter soil respiration on the eastern Tibetan Plateau of China. We therefore measured winter soil CO2fluxes and estimated annual soil respiration in two contrasting coniferous forest ecosystems(a Picea asperata plantation and a natural forest).Mean winter soil CO2effluxes were 1.08 lmol m-2s-1in the plantation and 1.16 lmol m-2s-1in the natural forest.These values are higher than most reported winter soil CO2efflux values for temperate or boreal forest ecosystems.Winter soil respiration rates were similar for our two forest ecosystems but mean soil CO2efflux over the growing season was higher in the natural forest than in the plantation. The estimated winter and annual soil effluxes for the natural forest were 176.3 and 1070.3 g m-2, respectively, based on the relationship between soil respiration and soil temperature,which were 17.2 and 9.7 % greater than their counterparts in the plantation. The contributions of winter soil respiration to annual soil efflux were 15.4 % for the plantation and 16.5 %for the natural forest and were statistically similar. Our results indicate that winter soil CO2efflux from frozen soils in the alpine coniferous forest ecosystems of the eastern Tibetan Plateau was considerable and was an important component of annual soil respiration. Moreover, reforestation(natural coniferous forests were deforested and reforested with P. asperata plantation) may reduce soil respiration by reducing soil carbon substrate availability and input.