Modelling Canopy Production. III. Canopy Light-Utilisation Efficiency and Its Sensitivity to Physiological and Environmental Variables

Abstract

A previously published model which predicts daily canopy photosynthesis from standard daily meteorological data and parameters of the single-leaf photosynthetic light-response curve is extended to predict annual canopy photosynthesis. The model is based on biologically plausible assumptions about canopy structure and assumes the single-leaf light response is a non-rectangular hyperbola of arbitrary shape. It uses simple algorithms for taking diurnal variation of temperature, and seasonal temperature acclimation of photosynthesis, into account. The model provides theoretical support for the observation that production by a canopy is proportional to irradiance intercepted or absorbed by the canopy. The model is used to explore the sensitivity of annual photosynthesis to parameters of the single-leaf light response. It is shown how the sensitivity of annual canopy photosynthesis to various factors can be determined from the sensitivity of parameters of the light response to the same factors. In particular, annual photosynthesis is shown to be sensitive to the effects of nutrition and temperature on light-saturated photosynthetic rate, and to seasonal temperature acclimation of photosynthesis. It is important that the variation with temperature, nutrition and season of parameters of the single-leaf light-response function be determined.