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Publication Date
1977
Description
Irrigated and water-stressed swards of perennial ryegrass were compared under field conditions to elucidate the physiological mechanisms which bring about the commonly observed reductions in dry matter (DM) yields caused by drought. Measurements were made during four periods of vegetative growth in the summers of two successive years. The maximum stress developed varied between 62 and 11 6 mm potential soil water deficit. In all but one experimental period, aboveground DM yield was markedly reduced, with corresponding reductions in leaf area index (LAI). The reduction in LAI was caused by a slower rate of leaf expansion> resulting in smaller leaves, and a slower rate of appearance. Canopy photosynthesis, on a ground area basis, was markedly lowered by water stress, thus explaining the lower rates ofDM production. However, the lower rate of photosynthesis could be accounted for by the reduction in leaf area in the stressed swards. Mean rates of photosynthesis, calculated by dividing the rates of canopy photosynthesis by LAI, indicated that there was little reduction in the rate of photosynthesis of individual leaves in the stressed compared with irrigated swards. This contrasts with controlled environment studies where a decline in canopy photosynthesis was attributed to a decline in individual leaf photosynthesis caused by stomata! closure. Calcu lation of canopy and leaf resistances from transpiration measurements confirmed that, in the field, stomata! closure is not a major factor reducing canopy photosynthesis.
Citation
Leafe, E L.; Jones, M B.; and Stiles, W, "The physiological effects of water stress on perennial ryegrass in the field" (1977). IGC Proceedings (1977-2023). 22.
(URL: https://uknowledge.uky.edu/igc/1977/sess1/22)
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The physiological effects of water stress on perennial ryegrass in the field
Irrigated and water-stressed swards of perennial ryegrass were compared under field conditions to elucidate the physiological mechanisms which bring about the commonly observed reductions in dry matter (DM) yields caused by drought. Measurements were made during four periods of vegetative growth in the summers of two successive years. The maximum stress developed varied between 62 and 11 6 mm potential soil water deficit. In all but one experimental period, aboveground DM yield was markedly reduced, with corresponding reductions in leaf area index (LAI). The reduction in LAI was caused by a slower rate of leaf expansion> resulting in smaller leaves, and a slower rate of appearance. Canopy photosynthesis, on a ground area basis, was markedly lowered by water stress, thus explaining the lower rates ofDM production. However, the lower rate of photosynthesis could be accounted for by the reduction in leaf area in the stressed swards. Mean rates of photosynthesis, calculated by dividing the rates of canopy photosynthesis by LAI, indicated that there was little reduction in the rate of photosynthesis of individual leaves in the stressed compared with irrigated swards. This contrasts with controlled environment studies where a decline in canopy photosynthesis was attributed to a decline in individual leaf photosynthesis caused by stomata! closure. Calcu lation of canopy and leaf resistances from transpiration measurements confirmed that, in the field, stomata! closure is not a major factor reducing canopy photosynthesis.
