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Hesketh, John D. Chen, Xiaoming 2011-05-07T13:45:26Z 2011-05-07T13:45:26Z 10000-01-01 1994 Soybean (Glycine max (L.) Merr. cv. Jack) was grown in the field in rain-protected plots to study effects of drought and atmospheric CO$\sb2$ enrichment on leaf gas exchange. Midday depressions in net leaf photosynthetic CO$\sb2$ 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$\sb2$ levels, stomatal limitations to Pn under drought stress were less important than at ambient atmospheric CO$\sb2$ levels. Morning and afternoon leaf starch levels were enhanced in both irrigated and nonirrigated plants in enriched CO$\sb2$. Afternoon starch levels were higher in stressed leaves than in non-stressed leaves at normal CO$\sb2$ 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$\sb2$ enrichment. Plants grown at 350-400 $\mu$L CO$\sb2$/L air and at 700-800 $\mu$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$\sb2$ level, but it was higher than that of ambient-grown plants when measured at elevated CO$\sb2$ 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$\sb2$ level; although the timing and extent of response differed, the general response pattern was identical. Gs values in plants grown in an enriched CO$\sb2$ environment responded differently to rapid changes in CO$\sb2$ than Gs values in ambient-grown plants; such behavior suggested stomatal acclimation to long-term exposure to an CO$\sb2$-enriched atmosphere. Leaf non-structural carbohydrate levels were greater in plants exposed to long-term atmospheric CO$\sb2$ 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$\sb2$-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$\sb2$-enrichment. Made available in DSpace on 2011-05-07T13:45:26Z (GMT). No. of bitstreams: 2 license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5) 9503163.pdf: 3872510 bytes, checksum: e4a18e3fd941e4cf2db4669ce15e5e55 (MD5) Previous issue date: 1994 Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding (hding2@illinois.edu) on 2011-05-07T14:58:47Z Item is restricted indefinitely. Restriction data tranferred 2014-07-01T11:27:41-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: ETDs are only available to UIUC Users without author permission Restricted to the U of I community indefinitely during batch ingest of legacy ETDs U of I Only AAI9503163 (UMI)AAI9503163 http://hdl.handle.net/2142/22610 eng Copyright 1994 Chen, Xiaoming Agriculture, Agronomy Biology, Ecology Biology, Plant Physiology Effects of elevated atmospheric carbon dioxide concentration and drought on soybean leaf photosynthesis text Agronomy Agronomy University of Illinois at Urbana-Champaign Dissertation Ph.D.