Gas exchange of carrot leaves in response to elevated CO2 concentration

Abstract

Short-term responses of four carrot (Daucus carota) cultivars: Cascade, Caro Choice (CC), Oranza, and Red Core Chantenay (RCC) to CO2 concentrations (Ca) were studied in a controlled environment. Leaf net photosynthetic rate (PN), intercellular CO2 (C i), stomatal conductance (gs), and transpiration rate (E) were measured at Ca from 50 to 1 050 μmol mol-1. The cultivars responded similarly to Ca and did not differ in all the variables measured. The PN increased with Ca until saturation at 650 μmol mol-1 (Ci = 350-400 μmol mol-1), thereafter PN increased slightly. On average, increasing Ca from 350 to 650 and from 350 to 1 050 μmol mol -1 increased PN by 43 and 52 %, respectively. The P N vs. Ci curves were fitted to a non-rectangular hyperbola model. The cultivars did not differ in the parameters estimated from the model. Carboxylation efficiencies ranged from 68 to 91 μmol m-2 s -1 and maximum PN were 15.50, 13.52, 13.31, and 14.96 μmol m-2 s-1 for Cascade, CC, Oranza, and RCC, respectively. Dark respiration rate varied from 2.80 μmol m-2 s-1 for Oranza to 3.96 μmol m-2 s-1 for Cascade and the CO2 compensation concentration was between 42 and 46 μmol mol-1. The gs and E increased to a peak at C a = 350 μmol mol-1 and then decreased by 17 and 15 %, respectively when Ca was increased to 650 μmol mol-1. An increase from 350 to 1 050 μmol mol-1 reduced gs and E by 53 and 47 %, respectively. Changes in gs and PN maintained the Ci:Ca ratio. The water use efficiency increased linearly with Ca due to increases in PN in addition to the decline in E at high Ca. Hence CO2 enrichment increases PN and decreases gs, and can improve carrot productivity and water conservation.