Ecosystem carbon exchanges of a subtropical evergreen coniferous plantation subjected to seasonal drought, 2003–2007

摘要

The behavior of whole ecosystems in humid climate zone in response todrought is less well documented. Continuous measurements of carbon dioxideand water vapor exchange using the eddy covariance technique during2003–2007 were made above a subtropical evergreen coniferous plantation inSoutheast China. Seasonal distribution of precipitation and temperature wasinconsistent during the summer, which resulted in droughts frequently. Grossecosystem photosynthesis (GEP), ecosystem respiration (RE) and net ecosystemproduction (NEP) showed clear seasonality, with low rates during droughtsand in winter. With statistical significance, the monthly GEP and REincreased exponentially with air temperature, but the monthly NEP was lesssensitive and only increased linearly with air temperature. However, thefunction response of monthly NEP and its components (GEP and RE) disappearedunder high temperature and low soil moisture. Monthly and yearly RE showed astatistically linear and positive dependence on the corresponding GEP.Annual NEP varied among years from 306 to 430 g C m−2 (mean 395, SD 50).Interannual variability in NEP was controlled primarily by airtemperature and the ratio of precipitation and evapotranspiration thataffected the RE/GEP ratio, which varied between 0.76 and 0.81 (mean 0.78,SD 0.02).