[Responses of net ecosystem carbon exchange to diffuse radiation in an alpine meadow on the Qinghai-Tibetan Plateau, China.].

Qinghai-Tibetan Plateau, one of the regions on the earth that receives the most solar radiation, is the world's highest alpine meadow ecosystem, with significance to regional and global carbon cycles. To examine the effects of solar radiation on ecosystem carbon dynamics in an alpine meadow, the net ecosystem CO exchange (NEE), solar radiation, diffuse radiation, and related environmental variables were measured using eddy-covariance technique and micro-meteorological system. Sky conditions were divided into three categories of clear days (CI≥0.7), cloudy days (0.315 ℃. Under clear sky day conditions, R increased with increasing CI due to the increases of air temperature, with negative effects on NEE. NEE increased with the increases of VPD up to 0.6 kPa, then slowly decreased when VPD>0.6 kPa, illustrating that NEE was reduced due to the relatively high VPD. Our results suggested that strong solar radiation on clear days would not increase carbon uptake capacity of alpine meadow, while cloudy days with clearness index of 0.6-0.7 would help increase carbon sequestration on the Qinghai-Tibetan Plateau.