GAS-EXCHANGE IN GREENHOUSE TOMATOES GROWN UNDER SUPPLEMENTAL LIGHT

This study reports on in situ gas-exchange measurements in tomatoes grown under a sequential intercropping system with supplemental lighting provided by high-pressure sodium-vapour lamps. A supplemental photosynthetic photon flux (PPF) of 150 mumol m-2 s-1 significantly increased the amount of light energy penetrating the canopy of intercropped tomato seedlings. During the day, the supplemental 150 mumol m-2 s-1 light regime increased the photosynthetic rate of leaves 5 and 10 by 67%, while at night the increases were 93 and 12%, respectively. Regression analysis of the photosynthetic rate of leaves 5 and 10 as a function of PPF received accounts for 58 and 45% of the variation, respectively. Hierarchical analysis demonstrated a significant linear relationship between PPF received during the day and photosynthetic activity of leaves 5 and 10 accounting for 46 and 28%, respectively, of the variance in the model. Regression analysis of the photosynthetic activity as a function of PPF received at night accounts for 41 and 32 %, respectively, of the variation in the photosynthetic rate of leaves 5 and 10. Using a high level of supplemental lighting during the day or at night had no significant effect on stomatic conductance or on the transpiration rate of leaves.