Effect of root-zone (RZ) CO2 on productivity and photosynthesis in aeroponically grown lettuce plants

Effects of root-zone (RZ) CO2 on crisphead-type lettuce (Lactuca sativa L. cv. 'Wintergreen' were 2 measured in an aeroponic system under photosynthetic photon F flux of 650 mumol m(-2) s(-1), 12 h photoperiod at 36degreesC/30degreesC and 28degreesC/22degreesC (day/night), with three enriched RZ CO2 levels (2000 ppm, 10,000 ppm and 50,000 ppm). Leaf growth was monitored after elevated RZ CO had been supplied for one week. Leaf areas with elevated RZ CO(2)were greater than ambient controls at both temperatures, while shoot and root weights were also higher. Increasing temperature reduced biomass overall, but the relative response to RZ CO2 was greater. Elevated RZ CO2 stimulated photosynthetic CO2 assimilation, with greater increase at higher temperatures. Elevated RZ CO2 decreased stomatal conductance at both temperatures, reducing transpiration water loss.