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Gas Exchange of Carrot Leaves in Response to Elevated CO2 Concentration
Authors:Kyei-Boahen  S.  Astatkie  T.  Lada  R.  Gordon  R.  Caldwell  C.
Affiliation:(1) Department of Plant and Animal Sciences, Nova Scotia Agricultural College, P.O. Box 550, Truro, NS, Canada, B2N 5E3;(2) Delta Research and Extension Center, Mississippi State University, P.O. Box 197, Stoneville, MS 38776, USA;(3) Department of Engineering, Nova Scotia Agricultural College, P.O. Box 550, Truro, NS, Canada, B2N 5E3
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 (Ci), stomatal conductance (gs), and transpiration rate (E) were measured at Ca from 50 to 1 050 mgrmol 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 mgrmol mol–1 (Ci= 350–400 mgrmol mol–1), thereafter PN increased slightly. On average, increasing Ca from 350 to 650 and from 350 to 1 050 mgrmol 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 mgrmol m–2 s–1 and maximum PN were 15.50, 13.52, 13.31, and 14.96 mgrmol m–2 s–1 for Cascade, CC, Oranza, and RCC, respectively. Dark respiration rate varied from 2.80 mgrmol m–2 s–1 for Oranza to 3.96 mgrmol m–2 s–1 for Cascade and the CO2 compensation concentration was between 42 and 46 mgrmol mol–1. The gs and E increased to a peak at Ca= 350 mgrmol mol–1 and then decreased by 17 and 15 %, respectively when Ca was increased to 650 mgrmol mol–1. An increase from 350 to 1 050 mgrmol 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.
Keywords:CO2 compensation concentration  cultivar differences  Daucus carota  net photosynthetic rate  nonlinear regression model  stomatal conductance  transpiration rate  water use efficiency
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