Carbon dioxide exchange between the atmosphere and an alpine shrubland meadow during the growing season on the Qinghai-Tibetan Plateau

In the present study, we used the eddy covariance method to measure CO2 exchange between the atmosphere and an alpine shrubland meadow ecosystem (37 degrees 36'N, 101 degrees 18' E; 3 250 in a.s.l.) on the Qinghai-Tibetan Plateau, China, during the growing season in 2003, from 20 April to 30 September. This meadow is dominated by formations of Potentilla fruticosa L. The soil is Mol-Cryic Cambisols. During the study period, the meadow was not grazed. The maximum rates Of CO2 uptake and release derived from the diurnal course of CO2 flux were -9.38 and 5.02 mu mol center dot m(-2)center dot s(-1), respectively. The largest daily CO2 uptake was 1.7 g C center dot m(-2)center dot d(-1) on 14 July, which is less than half that of an alpine Kobresia meadow ecosystem at similar latitudes. Daily CO2 uptake during the measurement period indicated that the alpine shrubland meadow ecosystem may behave as a sink of atmospheric CO2 during the growing season. The daytime CO2 uptake was correlated exponentially or linearly with the daily photosynthetic photon flux density each month. The daytime average water use efficiency of the ecosystem was 6.47 mg CO2/g H2O. The efficiency of the ecosystem increased with a decrease in vapor pressure deficit.