Photosynthetic gas exchange responses to light, temperature, carbon dioxide and water stress, and changes in photosynthetic pigments to light and water stress in two cultivars of Hordeum vulgare L

Logie, Malcolm Ronald Ruxton (1992) Photosynthetic gas exchange responses to light, temperature, carbon dioxide and water stress, and changes in photosynthetic pigments to light and water stress in two cultivars of Hordeum vulgare L. Masters thesis, Rhodes University.

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Abstract

The gas exchange responses of two cultivars of Hordeum vulgare L., to light, temperature, CO₂ and water stress were investigated in the laboratory. The optimum temperature for net CO₂ assimilation was found to be 25°C and 22.5°C for cv. Clipper and cv. Dayan respectively. Net CO₂ assimilation was reduced at 30°C in cv. Dayan. At low light intensity the highest quantum yield efficiency was 0.051 mol.mol⁻¹ at 30°C for cv. Clipper, and 0.066 mol.mol⁻¹ at 20°C for cv. Dayan. At the same temperature, cv. Clipper had a higher water use efficiency than cv. Dayan, but stomatal conductance for cv. Dayan was higher than cv. Clipper. Stomatal limitation to CO₂ was lowest at the optimum temperature for CO₂ assimilation in both cultivars. Stomata limited CO₂ assimilation in cv. Clipper to a larger degree than in cv. Dayan. Relative stomatal limitation for cv. Clipper at 25°C was 0.280 ± 0.010, and for cv. Dayan at 22.5°C was 0.028 ± 0.011. Short-term exposure to elevated CO₂ concentrations increased CO₂ assimilation in both cultivars, but more so for cv. Clipper. Transpiration rate at elevated CO₂ partial pressures were higher in cv. Dayan than in cv. Clipper. At very high CO₂ (860 μmol.m⁻²s⁻¹) partial pressure water use efficiency in cv. Clipper was higher than cv. Dayan, but at low CO₂ partial pressures water use efficiency in cv. Dayan was higher than cv. Clipper. Water stress reduced the relative leaf water content and net CO₂ assimilation in both cultivars. Cultivar Dayan was more tolerant to water stress, and CO₂ assimilation in this cultivar was less affected by water stress. In both cultivars water stress increased the concentration of chlorophyll a, chlorophyll b, and chlorophyll a+b. The chlorophyll a:b ratio remained relatively constant throughout the stress period. No correlation between relative leaf water content and total carotenoid concentration was observed.

Item Type:Thesis (Masters)
Uncontrolled Keywords:Gas exchange, Hordeum vulgare L, Light, Temperature, CO₂, Assimilation, Water, Stress, Use, Efficiency, Stomata, Leaf, Chlorophyll, Transpiration
Subjects:Q Science > QK Botany
Divisions:Faculty > Faculty of Science > Botany
Supervisors:Botha, C.E.J.
ID Code:4211
Deposited By: Philip Clarke
Deposited On:10 Dec 2012 07:50
Last Modified:10 Dec 2012 07:50
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