Seasonal dynamics of carbon dioxide exchange in a mixed grassland ecosystem

Abstract

Carbon dioxide exchange of a mixed grassland sward dominated by Agropyron dasystachyum and A. smithii was measured over two growing seasons using field chambers and infrared gas analysis. Net photosynthesis of the sward began in late April and rose to a peak in early July ([Formula: see text] ground area h−1). Drought during the later part of the summer, a typical feature of the climate of the region, caused net photosynthesis to decline drastically. Air temperature and reduced green leaf area inhibited photosynthesis early and late in the growing season. A multiple regression analysis showed that soil moisture and air temperature together accounted for 44% of the variability in net photosynthesis. Solar radiation and dew-point temperature explained an additional 16%. The ability of the dominant grasses to adapt to fluctuations in water availability is discussed.