A few programmes change the environmental settings so as to maximise leaf photosynthesis. A more productive approach might be to maximise crop photosynthesis but there is relatively little data available on which to base the settings.
In the experiments referred to below, the photosynthetic responses of entire crop canopies of Chrysanthemum and tomato were measured over a range of natural light conditions. For Chrysanthemum, canopy photosynthesis was measured at 23 degsC, 28 degsC and 33 degsC and 440ppm, 700ppm and 1,000ppm CO2. For tomato, the conditions were 23 degsC, 28 degsC and 32 degsC and 440ppm or 1,000ppm CO2. As expected, canopy photosynthesis increased both with increasing light and increasing CO2 concentration. However, the optimum temperature for Chrysanthemum photosynthesis was 28 degsC under high light/high CO2 and 29 degsC for tomato. When the CO2 concentration was lowered, the optimum for tomato fell to 27 degsC. For Chrysanthemum, it fell to below 23 degsC. These changes were much less than for leaf photosynthesis. Although it is feasible to control the aerial environment, responses of each crop will have to be determined separately.
Quantification of Temperature, CO2, and Light Effects on Crop Photosynthesis as a Basis for a Model-based Greenhouse Climate Control by Korner, Heuvelink and Niu (2009). Journal of Horticultural Science & Biotechnology 84 (2): 233-239. The authors' abstract of their manuscript can be seen in full at www.jhortscib.com.