Analysis of the spatial and temporal changes in soil CO2 flux in alpine meadow of Qilian Mountain

Field experiments on the CO2 flux of alpine meadow soil in the Qilian Mountain were conducted along the elevation gradient during the growing season of 2004 and 2005. The soil CO2 flux was measured using the Li-6400-09 soil respiration chamber attached to the Li-6400 portable photosynthesis system. The effects of water and heat and roots on the soil CO2 flux were statistically analyzed. The results show that soil CO2 flux along the elevation gradient gradually decreases. The soil CO2 flux was low at night, with lowest value occurring between 0200 and 0600 hours, started to rise rapidly during 0700-0830 hours, and then descend during 1600-1830 hours. The peak CO2 efflux appears during 1100-1600 hours. The diurnal average of soil CO2 efflux was between 0.56 +/- A 0.32 and 2.53 +/- A 0.76 mu mol m(-2) s(-1). Seasonally, soil CO2 fluxes are relatively high in summer and autumn and low in spring and winter. The soil CO2 efflux, from the highest to the lowest in the ranking order, occurred in July and August (4.736 mu mol m(-2) s(-1)), June and September, and May and October, respectively. The soil CO2 efflux during the growing season is positively correlated with soil temperature, root biomass and soil water content.