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Accueil du site → Doctorat → États-Unis → 1982 → ECOPHYSIOLOGICAL STUDIES OF THREE SPECIES FROM THE COLORADO SHORTGRASS STEPPE : PHYSIOLOGICAL FACTORS REGULATING DISTRIBUTION IN SPACE AND TIME

Washington State University (1982)

ECOPHYSIOLOGICAL STUDIES OF THREE SPECIES FROM THE COLORADO SHORTGRASS STEPPE : PHYSIOLOGICAL FACTORS REGULATING DISTRIBUTION IN SPACE AND TIME

Monson, Russell

Titre : ECOPHYSIOLOGICAL STUDIES OF THREE SPECIES FROM THE COLORADO SHORTGRASS STEPPE : PHYSIOLOGICAL FACTORS REGULATING DISTRIBUTION IN SPACE AND TIME

Auteur : Monson, Russell

Université de soutenance : Washington State University,

Grade : Doctor of Philosophy (PhD) 1982

Résumé
An analysis of the factors regulating photosynthesis in A. smithii was conducted through studies of leaf gas exchange and RuBP carboxylase activity to temperature. Below 40(DEGREES)C, temperature inhibition was primarily due to oxygen inhibition of photosynthesis, which reached a maximum of 65% at 45(DEGREES)C. Increases in values for the apparent Michaelis constant (Kc) for ribulose 1,5-bisphosphate (RuBP) carboxylase were observed to increase with increasing temperature in both in vitro and in vivo assays. The Q(,10) values for the maximum velocity (V(,max)) of CO(,2) fixation by RuBP carboxylase in vivo was lower (1.3-1.6) than those calculated from in vitro assays (1.8-2.2). The results suggest that temperature dependent changes in enzyme capacity may have a role in above-optimum temperature limitations below 40(DEGREES)C. At leaf temperatures above 40(DEGREES)C, decreases in photosynthetic capacity were partially dependent on temperature induced irreversible reduction in the quantum yield for CO(,2) uptake. Agropyron smithii exhibited superior photosynthesis rates at all analysis temperatures when grown in a cool temperature regime, relative to a warm temperature regime. Bouteloua gracilis exhibited higher photosynthesis rates when grown in the warmer temperature regime. Carex stenophylla demonstrated a capacity for photosynthetic temperature acclimation. Agropyron smithii exhibited the lowest range of high temperature damage thresholds, B. gracilis exhibited the highest values, and C. stenophylla was intermediate to the other species. Photosynthetic processes in B. gracilis were more sensitive to chilling temperature (0-12(DEGREES)C), relative to the other two species. The results demonstrate a correlation between photosynthetic temperature adaptation and in situ seasonal phenology patterns. Field measurements of photosynthesis and transpiration indicated higher water-use efficiencies and a more conservative "strategy" towards water-use in the C(,4) grass B. gracilis, relative to the other species. The results provide a physiological basis for this species occurring on arid upland sites, relative to the lowland mesic sites to which A. smithii is restricted.

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