LAUSR

Abstract Although soil respiration (Rs), as the largest flux of CO2 from terrestrial ecosystems to the atmosphere, has been measured and simulated widely, its drivers on different temporal scales in high-altitude regions are not well known. These driving factors were analysed at a site upstream of the Heihe River Basin based on measurements carried out using a field chamber over 3 years during three stages of the 5 cm soil layer: freezing and thawing (FT), completely frozen (CF), and completely thawed (CT). The analysis covered hysteresis with reference to soil respiration, photosynthesis, diurnal changes in soil temperature during CT in the growing season, and the contribution of carbon emissions outside the growing season (winter) to the total annual Rs. Results show that 1) the drivers of Rs on the diurnal scale during FT, CF, and CT were totally different: soil temperature (T5) and moisture (W5) at 5 cm depth for FT; air temperature near soil surface (Ta) and soil water content at 20 cm depth (W20) for CF, and T5 and photosynthetically active radiation (PAR) for CT; 2) at the diurnal scale during CT, Rs took 1.48–6.16 h less to reach its peak value than what T5 did, while 0.84–2.81 h more than PAR did; 3) cumulative Rs in winter was 132.31 g cm−2, accounted for approximately 16% of the annual carbon efflux from the subalpine meadow. Results suggest that the contribution of winter to the annual total Rs was large and should be considered in assessing carbon budget in high-altitude regions.