Effects of precipitation seasonal distribution on net ecosystem CO2 exchange over an alpine meadow in the southeastern Tibetan Plateau

Abstract

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 CO₂ 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^-2 month^-1), 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^-2 month^-1. Monthly CO₂ fluxes were mainly controlled by air temperature and soil water content. A large annual variation of CO₂ uptake was observed. The annual NEE was - 140.3 g C m^-2 year^-1 in 2014 while - 247.0 g C m^-2 year^-1 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 CO₂ uptake, while more precipitation concentrated in wet season depressed the meadow's light response through the decrease of the magnitude of light-saturated net CO₂ exchange (NEE_sat) at the onset and the end of growing season.

Keywords: Alpine meadow; Eddy covariance; NEE; Precipitation; Soil water content.