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 (Ci), 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 PNvs.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 Ca= 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. and S. Kyei-Boahen ... [et al.].
Response to irradiance of leaf net photosynthetic rates (PN) of four carrot cultivars: Cascade, Caro Choice (CC), Oranza, and Red Core Chantenay (RCC) were examined in a controlled environment. Gas exchange measurements were conducted at photosynthetic active radiation (PAR) from 100 to 1 000 μmol m-2 s-1 at 20 °C and 350 μmol (CO2) mol-1(air). The values of PN were fitted to a rectangular hyperbolic nonlinear regression model. PN for all cultivars increased similarly with increasing PAR but Cascade and Oranza generally had higher PN than CC. None of the cultivars reached saturation at 1 000 μmol m-2 s-1. The predicted PN at saturation
(PNmax) for Cascade, CC, Oranza, and RCC were 19.78, 16.40, 19.79, and 18.11 μmol (CO2) m-2 s-1, respectively. The compensation irradiance (I c) occurred at 54 μmol m-2 s-1 for Cascade, 36 μmol m-2 s-1 for CC, 45 μmol m-2 s-1 for Oranza, and 25 μmol m-2 s-1 for RCC. The quantum yield among the cultivars ranged between 0.057-0.033 mol(CO2) mol-1(PAR) and did not differ. Dark respiration varied from 2.66 μmol m-2 s-1 for Cascade to 0.85 μmol m-2 s-1 for RCC. As PN increased with PAR, intercellular CO2 decreased in a non-linear manner. Increasing PAR increased stomatal conductance and transpiration rate to a peak between 600 and 800 μmol m-2 s-1 followed by a steep decline resulting in sharp increases in water use efficiency. and S. Kyei-Boahen ... [et al.].