RESPONSE OF PHOTOSYNTHESIS AND CONDUCTANCE TO LIGHT, CO2, TEMPERATURE AND HUMIDITY IN TOMATO PLANTS ACCLIMATED TO AMBIENT AND ELEVATED CO2

In tomato (Lycopersicon esculentum L.) plants, net carbon dioxide exchange rate (P(N)) response curves to both irradiance (I) and short-term [CO2] were similar for plants grown at both 350 and 700 cm3(CO2) m-3. However, water vapor conductance (gH2O) of plants grown at high [CO2] was less sensitive to short term [CO2] variations, when measured at low vapor pressure difference, and was larger than the conductance of ''ambient [CO2]'' plants when both were exposed to high [CO2]. P(N) and g(H2O) under high I increased with temperature over the range 18 to 32-degrees-C. P(N) of plants grown in both [CO2] treatments increased at most about 25 % from 350 to 700 cm3 m-3 at 18 and 25-degrees-C, and decreased when exposed to 1000 cm3 m-3 at these temperatures. Thus increasing atmospheric [CO2] might not increase P(N) by as much as expected and water use of crops might not decrease.