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Diurnal Changes in Leaf Resistance to Water Vapor Diffusion at Different Heights in a Soybean Canopy 1
Author(s) -
Stevenson K. R.,
Shaw R. H.
Publication year - 1971
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/agronj1971.00021962006300010007x
Subject(s) - canopy , water content , agronomy , soil water , vapour pressure deficit , environmental science , moisture , diffusion , chemistry , transpiration , botany , soil science , biology , photosynthesis , geotechnical engineering , organic chemistry , physics , thermodynamics , engineering
The effect of soil moisture content and evaporative demand on diurnal variations of leaf resistance to water vapor diffusion were studied at two heights in a soybean ( Glycine max L. (Merr.)) canopy. Under soil moisture stress, leaf resistance to water‐vapor diffusion of middle leaves in the canopy increased approximately 2 hr earlier in the day and to a greater extent than the resistance of upper leaves. This indicated a preferential flow of water to upper leaves. It is speculated that the degree of out‐of‐phase change in leaf resistance under stress conditions is related to canopy density. Leaf resistances of middle leaves decreased at a slower rate under adequate soil water supply than under drier conditions. On days with low evaporative demand, leaf resistances of upper leaves tended to be less (0.8 sec/cm) under the low soil moisture than under the high soil moisture supply. The apparent reduction of stomatal activity in leaves under low evaporative demand and high soil moisture supply is believed related to the lack of development of a small leaf‐water deficit necessary for maximal stomatal opening.