Profile of Methane Concentrations in Soil and Atmosphere in Alpine Steppe Ecosystem on Tibetan Plateau

The methane concentration profile from -1.5m depth in soil to 32m height in air was measured in alpine steppe located in the permafrost area.Methane concentrations showed widely variations both in air and in soil during the study period.The mean concentrations in atmosphere were all higher than those in soil,and the highest methane concentration was found in air at the height of 16m with the lowest concentration occurring at the depth of 1.5m in soil.The variations of atmospheric methane concentrations did not show any clear pattern both temporally and spatially,although they exhibited a more steady-stable state than those in soil.During the seasonal variations,the methane concentrations at different depths in soil were significantly correlated (R2>0.6) with each other comparing to the weak correlations (R2<0.2) between the atmospheric concentrations at different heights.Mean methane concentrations in soil significantly decreased with depth.This was the compositive influence of the decreasing production rates and the increasing methane oxidation rates,which was caused by the descent soil moisture with depth.Although the methane concentrations at all depths varied widely during the growing season,they showed very distinct temporal variations in the non-growing season.It was indicated from the literatures that methane oxidation rates were positively correlated with soil temperature.The higher methane concentrations in soil during the winter were determined by the lower methane oxidation rates with decreasing soil temperatures,whereas methane production rates had no reaction to the lower temperature.Relations between methane contribution and other environmental factors were not discussed in this paper for lacking of data,which impulse us to carry out further and more detailed studies in this unique area.