Seasonal dynamics of carbon dioxide exchange in a mixed grassland ecosystem

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Abstract
Carbon dioxide exchange of a mixed grassland sward dominated by Agropyron dasystachyum and A. smithii was measured over 2 growing seasons using field chambers and IR gas analysis. Net photosynthesis of the sward began in late April and rose to a peak in early July (.simeq. 1.0 g CO2 m-2 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.

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