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Publication Date
1981
Description
Experiments were conducted to seek understanding of the adaptive characters that contribute to the success of the twining tropical legume siratro (Macroptilium atropurpureum) as a component of sown pastures in the seasonally dry tropics and subtropics of northeastern Australia. Siratro was grown both in the field and in controlled environments and was subjected to sequences of water stress. Measurements were made of tissue-water relations, leaf gas exchange, leaf movement, and leaf energy balance. Siratro avoids the effects of stress by maintaining its leaf-water potential greater than -20 bar, while grasses grown in association with it are about -60 to -80 bar. The tissues of siratro were not able to tolerate leaf-water potential less than about -24 bar. Siratro made only slight changes in its water relations and its stomata! response when exposed to a variety of water-stress treatments, either in the field or in controlled environments. Siratro has three main mechanisms by which it prevents leaf-water deficits from developing and by which it maintains relatively high leaf-water status. 1. It has good stomata! control over water loss; the stomata close at relatively high water potential and in reponse to falling atmospheric humidity independent of leaf-water potential. 2. Paraheliotropic leaf movements which operate to minimize the radiation received by the leaves and can result in their being 8°-10°C cooler than leaves held horizontal during water stress. The lower temperature reduces the vapor pressure gradient between leaf and air, and hence reduces water loss . .3. Shedding leaves reduces the amount of transpiring tissue. As the level of water stress increases, the older leaves are shed; new leaves are smaller, thicker, dark green, and hairy. If stress continues, whole branches die until only the crown remains, most of which is under the soil surface. While these mechanisms allow siratro to avoid severe leaf water deficits in many circumstances, its inability to withstand leaf water potentials less than -24 bar makes it vulnerable in extended drought periods. We believe that increasing the ability of siratro to tolerate water deficits could increase its survival and expand its utility.
Citation
Fisher, M J. and Ludlow, M M., "Responses of Siratro (Macroptilium atropurpureum) to Water Stress" (1981). IGC Proceedings (1981-2023). 7.
(URL: https://uknowledge.uky.edu/igc/1981/section6/7)
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Responses of Siratro (Macroptilium atropurpureum) to Water Stress
Experiments were conducted to seek understanding of the adaptive characters that contribute to the success of the twining tropical legume siratro (Macroptilium atropurpureum) as a component of sown pastures in the seasonally dry tropics and subtropics of northeastern Australia. Siratro was grown both in the field and in controlled environments and was subjected to sequences of water stress. Measurements were made of tissue-water relations, leaf gas exchange, leaf movement, and leaf energy balance. Siratro avoids the effects of stress by maintaining its leaf-water potential greater than -20 bar, while grasses grown in association with it are about -60 to -80 bar. The tissues of siratro were not able to tolerate leaf-water potential less than about -24 bar. Siratro made only slight changes in its water relations and its stomata! response when exposed to a variety of water-stress treatments, either in the field or in controlled environments. Siratro has three main mechanisms by which it prevents leaf-water deficits from developing and by which it maintains relatively high leaf-water status. 1. It has good stomata! control over water loss; the stomata close at relatively high water potential and in reponse to falling atmospheric humidity independent of leaf-water potential. 2. Paraheliotropic leaf movements which operate to minimize the radiation received by the leaves and can result in their being 8°-10°C cooler than leaves held horizontal during water stress. The lower temperature reduces the vapor pressure gradient between leaf and air, and hence reduces water loss . .3. Shedding leaves reduces the amount of transpiring tissue. As the level of water stress increases, the older leaves are shed; new leaves are smaller, thicker, dark green, and hairy. If stress continues, whole branches die until only the crown remains, most of which is under the soil surface. While these mechanisms allow siratro to avoid severe leaf water deficits in many circumstances, its inability to withstand leaf water potentials less than -24 bar makes it vulnerable in extended drought periods. We believe that increasing the ability of siratro to tolerate water deficits could increase its survival and expand its utility.
