Effects of elevated root-zone CO2 and root-zone temperature on productivity and photosynthesis of aeroponically grown lettuce plants

Abstract

Elevated root-zone (RZ) [CO2] resulted in significantly higher maximal photosynthetic CO2 assimilation rate (A) but lower stomatal conductance (gs) in aeroponically grown temperate lettuce in the tropics. Higher midday leaf relative water content (RWC) was observed at elevated RZ [CO2]. Grown at 20 °C-RZ temperature (RZT), all plants accumulated more biomass than at ambient (A)-RZT. The increase of biomass was greater in roots than in shoots supported by lower shoot/root ratio under elevated RZ [CO2]. The percentage increase in biomass under elevated RZ [CO2] was greater at A-RZT although the total biomass was higher at 20 °C-RZT. NO3− and total reduced N concentrations of shoot and root, total leaf soluble and Rubisco protein were significantly higher in all elevated RZ [CO2] plants than in ambine RZ [CO2] (360 ppm) at both RZTs. Roots, however, under each RZ [CO2] at A-RZT had significantly higher NO3− and total reduced N concentration than at 20 °C-RZT. At each RZ [CO2], total leaf soluble and Rubisco protein concentration was significant greater at 20 °C-RZT than at A-RZT.