Modelling Photosynthesis in Monocultures and Mixtures

Abstract

A comparison is made between two models of canopy photosynthesis for monocultures that differ in their treatment of the variation of the rate of single-leaf photosynthesis in response to the irradiance in which the leaves have grown. Both are shown to be deficient, and a simple modification to one that results in a much improved performance is presented. The theory uses the non-rectangular hyperbola for the rate of single-leaf photosynthesis and incorporates the Monsi-Saeki approach for the light-intercepting characteristics of the canopy. The model is then extended to describe the photosynthesis of mixed canopies, which requires knowledge of the relative position of each leaf-area component within the sward. Analytical expressions can be derived for the case where the leaf-area components are homogeneously distributed relative to each other through the depth of the canopy. This is shown to be a good representation of leaf-area distributions in continuously grazed temperate grass-clover swards as well as frequently cut tropical grass-legume swards, and so is an important special case.