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 (g_s) 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.