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

Abstract

Effects of root-zone (RZ) CO₂ on crisphead-type lettuce (<i>Lactuca sativa</i> L. cv. ‘Wintergreen’ were measured in an aeroponic system under photosynthetic photon flux of 650 μmol m^-2 s^-1, 12 h photoperiod at 36^oC/30^oC and 28^oC/22^oC (day/night), with three enriched RZ CO₂ levels (2000 ppm, 10,000 ppm and 50,000 ppm). Leaf growth was monitored after elevated RZ CO₂ had been supplied for one week. Leaf areas with elevated RZ CO₂ 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.