Abstract:

Aims Our objective was to understand seasonal and diurnal variations in CO₂ exchange of a grassland ecosystem by clarifying the carbon cycle and its affecting factors for a planted pasture ecosystem in the Sanjiangyuan Region of the Qinghai-Tibetan Plateau.

Methods We used the eddy covariance method to measure net ecosystem CO₂ exchange (NEE) and environmental factors in the planted pasture (Elymus nutans) ecosystem in 2006.

Important findings Daily maximum uptake and release of CO₂ were 6.56 and -4.87 g CO₂·m^-2·d^-1, respectively. Maximum rates of NEE uptake and release were -0.35 and 0.22 mg CO₂·m^-2·s^-1, respectively. Annual gross primary production (GPP) was 1 761 g CO₂·m^-2·a^-1, of which more than 90% was consumed by ecosystem respiration (R_eco). Annual NEE was -111 g CO₂·m^-2. In the growing season, maximum and minimum R_eco/GPP values were 90% in May and 79% in June, respectively. The Q₁₀ was 4.81, which is higher than in other ecosystems. The NEE was mostly influenced by photosynthetic photon flux density (PPFD), temperature and vapor pressure deficit (VPD). The R_eco was mainly affected by soil temperature at 5 cm depth (T_s).

Key words: eddy covariance, gross primary production (GPP), net ecosystem CO₂ exchange (NEE), planting pasture, Qinghai-Tibetan Plateau