Energy exchange phenomena, physiological rates and leaf size variation

Leaf temperatures have often been observed to crossover air temperatures in such a way that they vary less than air temperature. The significance of this bevavior to optimal leaf size is examined both from the aspect of energy balance and leaf photosynthesis and transpiration. Larger leaves are shown to be buffered more from air temperatures than smaller leaves, but this benefit is more than offset by reductions in photosynthesis. Under certain conditions, however, leaf temperature and photosynthesis is leaf size independent. The location of this size independent behavior along an air temperature gradient is related to changes in leaf resistance and suggests a mechanism by which high levels of leaf size variation are maintained in plants and leads to the prediction that leaf size variation is greater in mesophytic species than in xerophytic species.