Effects of precipitation seasonal distribution on net ecosystem CO exchange over an alpine meadow in the southeastern Tibetan Plateau.

Ecosystem carbon balance might be affected by the variability of seasonal distribution of precipitation under global climate change. Using the eddy covariance (EC) technique, long-term observations of ecosystem net CO exchange (NEE) were acquired over Lijiang alpine meadow in the southeastern Tibetan Plateau from January 2014 to August 2019. During the wet season (from June to October), Lijiang meadow functioned as a carbon sink (- 37.6 ± 22.5 g C m month), while in dry season, the meadow varied between a weak carbon source and sink with an average monthly NEE of - 3.9 ± 11.9 g C m month. Monthly CO fluxes were mainly controlled by air temperature and soil water content. A large annual variation of CO uptake was observed. The annual NEE was - 140.3 g C m year in 2014 while - 247.0 g C m year in 2016. Correspondingly, the precipitation in wet season accounted 90% of annual precipitation in 2014 and 74% of that in 2016 despite the annual precipitation was larger than 1200 mm in both years. More precipitation in dry season can lead to longer period of net CO uptake, while more precipitation concentrated in wet season depressed the meadow's light response through the decrease of the magnitude of light-saturated net CO exchange (NEE) at the onset and the end of growing season.