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Leaves of Piper auritum H.B. & K., a tropical forest tree common in large gaps and clearings, quickly wilted when exposed to full sun. One consequence of this wilting was a dramatic reduction in the projected leaf area normal to the direct solar beam. As a result, intercepted photosynthetically active radiation decreased by 50-70%, and leaf temperature decreased by 1-5 GC, which led, respectively, to decreased photosynthesis and transpiration. Because the decrease in photosynthesis was smaller than the decrease in transpiration, wilting resulted in an increase in the ratio of photosynthesis to transpiration (wateruse-efficiency), relative to leaves prevented from wilting. Stomatal conductance decreased when leaves were exposed to high light but did not change dramatically when leaves wilted. By affecting the leaf-air vapour concentration gradient, partial stomatal closure further enhanced the effects of wilting on water-use-efficiency. Key-words: Piper auritum, wilting, water-use-efficiency
Chiariello et al. (Thu,) studied this question.