Effect of high CO concentration upon photosynthesis in tropical species

The large amount of information on the effects of an experimental increase in [CO2] on the physiology of plants in temperate zones is in contrast with the scant information available on tropical plants. In view, of this, the photosynthetic responses to elevated [CO2] of plants growing in Venezuela w ere studied. In order to elucidate the effect of elevated [CO2] on the phot osynthesis and water use of species that are normally subjected to water de ficit, plants of four xerophytic species were grown under elevated [CO2]. P hotosynthesis increased approximately 3.5 times and elevated [CO2] delayed the decrease of photosynthetic rate under drought. Since in many studies th e initial promotion of photosynthetic rate caused by elevated [CO2] has bee n observed to disappear in tune clue to limitations imposed by the sinks, w e studied the effect of elevated [CO2] on the photosynthesis of cassava pla nts grown without soil limitations. Photosynthetic rate did not decrease at any time during the growth cycle of the crop. The occurrence of a large si nk (the root) together with a sufficiently large volume of substrate permit ted the maintenance of a higher photosynthetic rate due to elevated [CO2]. The effect of very high [CO2] on photosynthesis was evaluated in wild plant s growing near natural sources; such high [CO2] did not inhibit the photosy nthetic rate and promoted it swell above that of controls.