The ecological significance of leaf movements in Rhododendron maximum

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Virginia Polytechnic Institute and State University

Although leaf movements have been documented for over a century, there are few studies focused on the adaptive significance of leaf movements, especially with experiments under controlled conditions. The major objective in this study is to determine the ecological significance of leaf movements in Rhododendron maximum, which is a subcanopy, evergreen species distributed in seasonally cold environments. Leaf movements could be necessary for maintaining a favorable energy balance and/or avoiding photoinhibition and photooxidation. A series of leaf manipulation treatments were established to verify these potential explanations. These leaf treatments were designed to separate the influence of leaf curling and leaf angle on leaf energy budget, gas-exchange characteristics, chlorophyll contents and leaf longevity.

Leaf movements were found to have a significant influence on leaf physiology and longevity of R. maximum. Without changes in leaf angle, chlorophyll contents decreased, and permanent photoinhibition occurred due to excess irradiance absorption in the winter. Leaf angle also influenced leaf temperature although the changes in leaf temperature were within the physiological tolerances of R. maximum leaves. Leaf curing had little or no effect on the parameters measured in the study.