Light-Mediated Reduction in Photosynthesis in Closed Greenhouses Can Be Compensated for by CO(2) Enrichment in Tomato Production

Concepts of semi-closed greenhouses can be used to save energy, whereas their technical equipment often causes a decrease in the light received by the plants. Nevertheless, higher yields are achieved, which are presumably triggered by a higher CO(2) concentration in the greenhouse and associated higher photosynthesis because of the technical cooling and the longer period of closed ventilation. Therefore, we examined the effects of photosynthetic photon flux density (PPFD) and CO(2) concentration on plant photosynthesis and transpiration in tomato using a multiple cuvette gas exchange system. In a growth chamber experiment, we demonstrated that a light-mediated reduction in photosynthesis can be compensated or even overcompensated for by rising CO(2) concentration. Increasing the CO(2) concentration from 400 to 1000 µmol mol(−1) within the PPFD range from 303 to 653 µmol m(−2) s(−1) resulted in an increase in net photosynthesis of 51%, a decrease in transpiration of 5 to 8%, and an increase in photosynthetic water use efficiency of 60%. Estimations showed that light reductions of 10% can be compensated for via increasing the CO(2) concentration by about 100 µmol mol(−1) and overcompensated for by about 40% if CO(2) concentration is kept at 1000 instead of 400 µmol mol(−1).