Simulating the dynamics of leaf physiology and morphology with an extended optimality approach

Abstract

On both a seasonal and single canopy scale several physiological and morphological leaf characteristics show significant variations for a wide range of species. Aiming at a better understanding, as well as predictions of spatial and temporal leaf adjustments, a recently proposed dynamic optimality approach is adapted to a set of relevant leaf variables. The underlying formalism explicitly includes the adaptive dynamics of an arbitrary growth controlling trait. The approach is based on the calculation of growth gradients, and hence requires functional growth dependencies on the traits as well as on the different environmental conditions within a crown. These dependencies are quantified using a standard photosynthesis model (PGEN). It is found that the simple gradient approach fails in describing patterns originating from leaf senescence. To include aging phenomena the model is completed by a simple evolution equation which is applicable for a wide range of species. Simulation results of the combined model for shaded and for sunlit reaves are compared to an existing dataset for beech phenology collected during 3 years at the Solling site in central Germany. The good overall correspondence, together with the small number of uncertain parameters, demonstrate a high efficacy of the model. It can thus be regarded as a valuable tool for assessing the annual canopy carbon assimilation as well as the adaptive significance of leaf variability. (C) 2000 Annals of Botany Company.