Effect of Water Stress on the Temperature Optima of Net CO2 Exchange for Two Desert Species |
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Authors: | PARK S. NOBEL DAVID J. LONGSTRETH TERRY L. HARTSOCK |
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Affiliation: | Department of Biology and Division of Environmental Biology of the Laboratory of Nuclear Medicine and Radiation Biology, University of California, Los Angeles, California 90024 |
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Abstract: | The temperature dependence of net CO2 exchange was determined at various soil water potentials for two sympatric desert species. Notholaena parryi D. C. Eat. (Pteridaceae) and Encelia farinosa Gray (Compositae). As water stress increased, the temperature optimum of apparent (net) photosynthesis shifted 7 to 10°C downward and the maximum rate decreased for both species. The downward shift in temperature optimum with water stress was the result of a greater fractional stomatal closure with increasing temperature and a lowering of the temperature where maximal CO2 residual conductance of the mesophyll cells occurred. This lowering of the temperature for maximal CO2 residual conductance appears to reflect (1) a greater effect of water stress on gross photosynthesis than on respiration plus photorespiration and (2) the higher temperature optimum for respiration plus photorespiration than for gross photosynthesis. The downward shift in the temperature optimum of apparent photosynthesis can have a significant effect on the predicted carbon balance of plants as the soil water potential decreases. |
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