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Influence of Leaf Age, Illumination, and Upper and Lower Surface Differences on Stomatal Resistance of Sugar Beet (Beta vulgaris) Leaves¹

Stomatal diffusion resistances of sugar beet leaves were calculated from measurements made on photomicrographs of leaf impressions. The impressions were made by spraying a rapid drying acrylic resin on the leaf.

Milthorpe and Penman's (1967) method for calculating Stomatal resistances was programed for electronic computer. Resistances were calculated for leaves of different physiological age and for shaded and sunlit leaves. Calculations were also made separately for upper and lower surfaces of selected leaves. Despite the continuous expansion of the sugar beet leaf throughout its life, the Stomatal resistance of similarly exposed leaves was independent of physiological age except for the most immature leaves.

The greater values of stomatal resistance found for older leaves in the lower part of the canopy were attributed to microclimatic differences, including reduced illumination, rather than to changes associated with advancing physiological age.

Key Words: Stomatal impressions

² Instructor and Professor, Agricultural Climatology, Departmen: of Horticulture and Forestry, University of Nebraska, Lincoln, Nebraska 68503.

Received for publication May 10, 1969.