Transpiration Rates of Fraxinusamericana and AcersaccharumLeaves

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Abstract
Experiments were conducted in the greenhouse and under constant environmental conditions on transpiration rates and stomatal aperture of intact seedlings and excised leaflets or leaves of Fraxinusamericana and Acersaccharum. Leaf surfaces of both species were studied with scanning electron microscopy. Transpiration rates on a leaf area or dry weight basis were consistently higher for Fraxinus than for Acer seedlings. Transpiration rates also were higher in excised leaves of Fraxinus than in those of Acer. The higher transpiration capacity of Fraxinus was associated with larger (but fewer) stomata, less efficient stomatal closure, and less effective cutinization than in Acer. Differences in transpiration rates between Fraxinus and Acer were greater for excised leaves than for intact seedlings. This was largely the result of more rapid stomatal closure of excised leaves of Acer than of Fraxinus. The paramount importance of control of stomatal aperture in influencing internal water balance of plants is emphasized.

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