Simulation of photosynthetic plasticity in response to highly fluctuating light: an empirical model integrating dynamic photosynthetic induction and capacity

Abstract 

An empirical model was developed to simulate photosynthetic responses of leaves to highly fluctuating light, with a special focus on the functional role of photosynthetic induction and capacity. Based on diurnal courses of light as input data, which were recorded at natural plant sites, we applied this model to simulate the corresponding course of net photosynthesis (output data) for leaves of two neotropical tree species. All six model input parameters (leaf-specific) were obtained via measurements of leaf gas exchange. The model was tested for leaves in their natural environments, characterized by frequent light-flecks. We compared measured carbon gains with computed ones, using a standard steady-state and our induction model. Simulation runs with the steady-state model can result in an immense overestimation of the true situation, by 13.4% at open sites [pioneer species Heliocarpus appendiculatus (Turczaninow)] and by 86.5% at low light environments of the understorey [mid to late successional species Billia colombiana (Planchon and Lindley)]. These significant overestimations, particularly in the understorey, are mainly the consequence of neglecting a dynamic photosynthetic induction under fluctuating light conditions. The model presented here resulted in clearly improved predictions; in open and understorey sites the true carbon gain of leaves was computed with a mean error of less than 7%. As most leaves at natural plant sites are exposed to light environments allowing for dynamic rather than steady-state CO₂ assimilation, the significance of such induction models is evident and is discussed in relation to scaling-up from leaf to canopy and to the whole plant indicating a large potential for errors.