Tansley Review No. 59 Leaf boundary layers.

Studies of heat and mass exchange between leaves and their local environment are central to our understanding of plant-atmosphere interactions. The transfer across aerodynamic leaf boundary layers is generally described by non-dimensional expressions which reflect largely empirical adaptations of engineering models derived for flat plates. This paper reviews studies on leaves, and leaf models with varying degrees of abstraction, in free and forced convection. It discusses implecations of finding for leaf morphology as it affects - and is affected by - the local microclimate. Predictions of transfer from many leaves in plant communities are complicated by physical and physiological feedback mechanisms between leaves and their environment. Some common approaches, and the current challenge of integrating leaf-atmosphere interactions into models of global relevance, are also briefly addressed. Contents Summary 477 I. Introduction 478 II. Early studies 479 III. The formal description of leaf transfer 480 IV. Effects of turbulence on idealized shapes 484 V. Effects of aspect ratio and inclination 486 VI. Leaves and leaf models in forced convection 491 VII. Leaves and leaf models in mixed and free convection 493 VIII. Interpretation of leaf shape 494 IX. Leaves in plant canopies 499 X. Synopsis and conclusions 502 References 502.