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Atmospheric concentrations of CO2 and O3 are increasing, which is expected to affect light-use efficiency (LUE) and yield of crops. We derive a mathematical formula for crop LUE as a function of CO2, temperature, light intensity and the Rubisco content of upper leaves. A corollary formula is derived that expresses the sensitivity of crop growth rate to changes in Rubisco, under various conditions. Both formulas were incorporated in an existing wheat model, together with new equations that represent the effects of O3. Five parameters were defined that quantify O3 relations: (1) the amount of Rubisco damaged per unit O3, (2, 3) rate and metabolic costs of O3 detoxification, (4, 5) rate and costs of repair. For quantification of the damage coefficient and repair rate, equations were developed that can be applied to gas exchange measurements in plants subjected to stepwise increase in ambient ozone concentration. The model was parameterised for spring wheat using literature data. Model simulations were carried out for various time courses of O3, CO2, temperature, light intensity, to explain reports in the literature on variation in crop response to elevated CO2 and O3 under different climatic conditions. In spite of model simplicity, simulations explained much of reported variation in crop response to elevated levels of CO2 and O3. The need and use of additional experimentation is discussed, as is the scope for analysing plant defence strategies in terms of investment in detoxification and repair. |
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