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Soybean Leaf Gas‐Exchange Responses to Carbon Dioxide and Water Stress
Author(s) -
Allen L. H.,
Valle R. R.,
Mishoe J. W.,
Jones J. W.
Publication year - 1994
Publication title -
agronomy journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 131
eISSN - 1435-0645
pISSN - 0002-1962
DOI - 10.2134/agronj1994.00021962008600040009x
Subject(s) - transpiration , carbon dioxide , stomatal conductance , photosynthesis , water use efficiency , chemistry , cuvette , zoology , irrigation , horticulture , vapour pressure deficit , agronomy , biology , physics , organic chemistry , quantum mechanics , biochemistry
As global carbon dioxide concentrations rise, we need to understand the combination of direct effects of this gas and the anticipated effects of climate change, including drought, on physiology and growth of all crops. Effects of CO 2 on plants begin at the leaf level; our objectives, therefore, were to determine interrelationships among factors governing gas exchange responses of soybean [ Glycine max (L.) Merr.] leaves to elevated CO 2 and water stress. Photosynthetic CO 2 assimilation and transpiration rates were measured in cuvettes on leaflets of soybean (cv. Bragg) grown in controlled‐environment chambers at 330 and 660 μmol CO 2 mol −1 air. Leaflets at high CO 2 , either water‐stressed or wellwatered, had higher photosynthetic and lower transpiration rates, and therefore higher water‐use efficiencies (WUE), than those at control CO 2 levels. As irrigation was withheld during an ll‐d period, WUE decreased about 30 to 50% with respect to the well‐watered treatments. Midday leaf temperature and leaf‐to‐air vapor pressure gradient levels increased as the water stress progressed. For water stress treatments, midday leaf conductance ( G tw ) was generally higher and residual internal conductance ( G r ) was generally lower in low than in high CO 2 . Ratios of midday G r / G tc were nearly constant throughout the period in both the stressed and the well‐watered treatments. The ratios of intercellular C i , to ambient C a , CO 2 concentration (i.e., C i / C a ) during the water stress period remained similar to the respective nonstressed treatments within each CO 2 level. These findings support the concept that leaf conductances are governed by CO 2 assimilation rates under water‐stressed as well as unstressed conditions.