Impact of atmospheric CO2 concentration on water use efficiency of maize

The effects of elevated CO2 concentration on plant transpiration and water use efficiency were studied in maize (Zea mays L.) Data concerned both the daytime and the entire crop life cycle, Maize plants were grown in two sepa rate compartments of a ventilated greenhouse. The first had normal ambient CO2 in the second CO2 was enriched to about double! the normal level. Two c rop periods were Studied, in 1992 and 1993, with continuous CO2 enrichment from seed to harvest. Continuous transpiration measurements were carried ou t plant by plant, Daily transpiration of plants increased with leaf growth. Doubling CO2 induced a decrease in daily plant transpiration. Over the ent ire crop life, the daily mean transpiration decrease was of The decrease in cumulated transpiration was of 17% too. Doubling CO2 induced a 23% increas e in water use efficiency (dry weight cumulated transpiration). There was n o difference in grain production. Thus, it is suggested that the increase i n maize biomass induced by elevated CO2 concentration could be explained by the decrease in water needs.