A real understanding of how the environmental factors affect gas exchange is extremely important for the optimization of CO2 photosynthetic assimilation and water loss control. In order to contribute to this, in two seasons, October 2002 and January 2003, the gas exchange and the potential photochemical efficiency in 'Formosa' papaya plants cultivated under field condition in São Francisco do Itabapoana, Rio de Janeiro State, were studied. The CO2 photosynthetic assimilation (A), stomatal conductance (gS), photosynthetic photon flux density (PPFD) were evaluated daily, four days per month, each every hour, from 8 a.m. to 5 p.m. In addition, the potential photochemical efficiency was measured from the same leaves and at the same conditions as before. The CO2 photosynthetic assimilation was higher in January. This result was due to a greater stomatal aperture on leaves of plants cultivated during this season. The lower A value observed in October, caused by the reduction of gS, was due to a higher photosynthetic photon flux density (Cloudless days) occurred in this month. Under the experimental conditions, measuring the potential photochemical efficiency, the photoinhibitory chronic type effect was not verified. Possibly the non-detection of damage to the photosynthetic apparatus has been due to the paraheliotropic movement of leaves, observed at warmer periods of the day. These results can contribute significantly for the papaya tree management grown under field condition, since any management strategy that optimizes the stomatal aperture will help the CO2 photosynthetic assimilation, and may result in an increase of productivity.
Carica papaya L.; gas exchange; photochemical efficiency
