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Accueil du site → Doctorat → Royaume-Uni → 1994 → Physiological responses to water stress in some tropical arid zone grasses

University of Wales, Aberystwyth (1994)

Physiological responses to water stress in some tropical arid zone grasses

Dast, A.A

Titre : Physiological responses to water stress in some tropical arid zone grasses

Auteur : Dast, A.A

Université de soutenance : University of Wales, Aberystwyth

Grade : Doctor of Philosophy (PhD) 1994

How do plants survive and grow in essential water shortage and adverse soil conditions of desert ecosystems ? To attempt to answer this question, four plant species (Cenchrus ciliaris L., Cenchrus pennisetiformis Hochst. et Steud., Panicum turgidum Forssk. and Lasiurus sindicus Henr.), from desert plant communities and one from habitats subjected to periodic flooding (Echinochloa colonum L. Link) were grown from seed and a growth analysis was carried out. This was complemented by measurements of net photosynthetic rate, dark respiration and leaf water potential. There were significant species differences in all the production parameters (RGR and biomass allocation to different organs), net photosynthetic rate, respiration rate and leaf water potential. In experiments with limited water supply or with salt application, the RGR of all the species was reduced, but the potentially fast growing (in terms of RGR) species (Panicum) still grew faster than the inherently slow growing species (Echinochloa). There were very few differences between these species in net assimilation rate (NAR), and the factor that best explained the differences in RGR was the leaf area ratio (LAR). This correlation was mainly due to the leaf weight ratio, the fraction of plant biomass allocated to leaf, and to lesser extent caused by the specific leaf area, the ratio between leaf area and leaf weight. Although net rates of photosynthesis decreased by droughting and recovered to the level of the normal plants in all the three species by rewatering, fast growing Panicum showed higher rate of photosynthesis than the other two species. Respiration response to droughting and rewatering different from the photosynthesis and RGR, but the species characterised by high RGR showed low rates of respiration. It is postulated that natural selection in arid environments has favoured species with a high SLA, LWR, and consequently a high leaf area ratio, whereas selection in nutrient poor habitats (washed and leached soils of seasonally flooded areas) has led to species with an inherently low LAR.

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