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Leaf Pubescence Effects on the Mass and Energy Exchange Between Soybean Canopies and the Atmosphere¹

Mass and energy exchanges with the atmosphere were compared in two soybean (Glycine max L. Merr. cv. Harosoy) isolines differing in pubescence density. The study was conducted in a field with a Sharpsburg silty clay loam soil (fine, montmorillonitic, mesic Typic Argiudoll) during the summer of 1980 at Mead, Nebr. Mass and energy exchanges were determined by means of micrometeorological techniques. Evapotranspiration (reported in terms of latent heat flux) was reduced in the densely pubescent isoline. Canopy CO₂ exchange was unchanged on a per unit land area basis. Water use efficiency (reported in terms of the CO₂-water flux ratio) was, accordingly, greater in the densely pubescent isoline. The increase in pubescence did not significantly alter the net radiation balance, turbulent mixing, canopy CO₂ exchange, or plant water status. Observed differences in the partitioning of net radiation into latent and sensible heat can be explained by greater penetration of solar radiation into the densely pubescent canopy. Leaf pubescence appears to alter the spectral characteristics of the leaf and, thus, to facilitate the penetration of solar radiation into the canop.

Key Words: Photosynthesis • Evapotranspiration • Water use efficiency • Canopy aerodynamics • Glycine max L.

² Formerly research associate (now Postdoctoral Fellow at the Atmospheric Turbulence and Diffusion Lab., P.O. Box E, Oak Ridge, TN 37830), associate professor, professor, professor and visiting scientist (Conicet, Argentina), Center for Agricultural Meteorology and Climatology and associate professor, Dep. of Agronomy, Institute of Agriculture and Natural Resources, Univ. of Nebraska, Lincoln, NE 68583-0728.

Received for publication March 31, 1982.