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University of Illinois at Urbana-Champaign (1994)

Effects of elevated atmospheric carbon dioxide concentration and drought on soybean leaf photosynthesis

Chen, Xiaoming

Titre : Effects of elevated atmospheric carbon dioxide concentration and drought on soybean leaf photosynthesis

Auteur : Chen, Xiaoming

Université de soutenance : University of Illinois at Urbana-Champaign

Grade : Doctor of Philosophy (PhD) 1994

Résumé
Soybean (Glycine max (L.) Merr. cv. Jack) was grown in the field in rain-protected plots to study effects of drought and atmospheric CO\sb2 \sb2 enrichment on leaf gas exchange. Midday depressions in net leaf photosynthetic CO\sb2 \sb2 exchange rates (Pn) were found in drought-stressed plants and the diurnal changes were mostly stomatal regulated, although accumulated drought stress eventually resulted in some non-stomatal limitations. However, seasonal changes in Pn were mostly limited by non-stomatal factors. Water use efficiency was always higher for drought stressed plants and depended on the severity of stress and associated stomatal or nonstomatal limitations. At enriched atmospheric CO\sb2 \sb2 levels, stomatal limitations to Pn under drought stress were less important than at ambient atmospheric CO\sb2 \sb2 levels. Morning and afternoon leaf starch levels were enhanced in both irrigated and nonirrigated plants in enriched CO\sb2 \sb2 . Afternoon starch levels were higher in stressed leaves than in non-stressed leaves at normal CO\sb2 \sb2 levels. Soybean (Glycine max (L.) Merr. cv. Jack) grown under both controlled environment and field conditions was used to study acclimation of leaf photosynthesis to long-term atmospheric CO\sb2 \sb2 enrichment. Plants grown at 350-400 μ μ L CO\sb2 \sb2 /L air and at 700-800 μ μ L/L were switched back and forth between treatments to follow dynamic changes in Pn and Gs. Pn of enriched plants was less than that of ambient-grown plants when measured at the ambient CO\sb2 \sb2 level, but it was higher than that of ambient-grown plants when measured at elevated CO\sb2 \sb2 levels, in both controlled environment and field studies. Stomatal conductance (Gs) of leaves on field-grown plants and pot-grown plants responded similarly to changes in air CO\sb2 \sb2 level ; although the timing and extent of response differed, the general response pattern was identical. Gs values in plants grown in an enriched CO\sb2 \sb2 environment responded differently to rapid changes in CO\sb2 \sb2 than Gs values in ambient-grown plants ; such behavior suggested stomatal acclimation to long-term exposure to an CO\sb2 \sb2 enriched atmosphere. Leaf non-structural carbohydrate levels were greater in plants exposed to long-term atmospheric CO\sb2 \sb2 enrichment, but we could not prove that this was the main cause for lower photosynthetic performance when such plants were placed in ambient air. Pn of CO\sb2 \sb2 enriched plants in ambient air did recover to that of ambient-grown plants after 15 days of exposure to ambient air. Both field-grown and pot-grown plants in controlled environments acclimated similarly to CO\sb2 \sb2 enrichment.

Mots Clés : Agriculture, Agronomy — Biology, Ecology — Biology, Plant Physiology

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