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Transpiration Rate and Water Use Effeciency of Soybean Leaves Adapted to Different CO 2 Environments 1
Author(s) -
Valle Raul,
Mishoe J. W.,
Jones J. W.,
Allen L. H.
Publication year - 1985
Publication title -
crop science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.76
H-Index - 147
eISSN - 1435-0653
pISSN - 0011-183X
DOI - 10.2135/cropsci1985.0011183x002500030011x
Subject(s) - transpiration , water use efficiency , horticulture , carbon dioxide , biology , stomatal conductance , botany , loam , diurnal temperature variation , zoology , photosynthesis , soil water , atmospheric sciences , ecology , geology
Gas exchange rates were measured during podfill on leaflets of soybean [ Glycine max (L.) Merr. ‘Bragg’] plants grown in 330 (ambient) and 660 (high) μmol CO 2 −1 environments in outdoor growth chambers and rooted in a reconstituted profile of Arredondo fine sand (loamy, siliceous, hyperthermic Grossarenic Plaleudult). Carbon exchange rates (CER), transpiration rates (TR), leaf resistance ( r L ) and leaf temperature ( T L ) measured to investigate their diurnal changes. These parameters were also measured during midday periods at various CO 2 concentrations (90‐990 μmol CO 2 mol −1 ) to study the effects of adaptation to ambient and high CO 2 , environments on the subsequent response to CO 2 levels. The primary objective was to determine CO 2 effects on leaf water use and water‐use efficiency, an important question as global CO 2 continues to rise. Diurnal TR of leaflets grown and measured at high CO 2 levels was not different from TR of leaflets grown and measured at ambient CO 2 . Leaf temperature was approximately 1.5°C higher for the leaflets at the high CO 2 concentration; also, r L was higher throughout the day on these leaflets than r L of those at ambient CO 2 levels. Water use efficiency (WUE = CER/TRf) or leaflets at high CO 2 was about twice the WUE of leaflets grown and measured at ambient CO 2 . Transpiration rates of leaflets adapted to ambient or high CO 2 concentrations were not significantly affected by short‐term CO 2 changes. However, regardless of CO 2 level of adaptation, T L and r L increased as CO 2 increased. It was concluded that: (i) TR of the high CO 2 leaflets was similar that of ambient CO 2 leaflets because the increases in r L caused by high CO 2 were partially offset by increases in vapor pressure gradient between leaf‐to‐air caused by increased T L ; (ii) Leaves adapted to high CO 2 had higher WUE than leaves adapted to ambient CO 2 , mainly because of a two‐fold increase in CER.