A Model for Leaf Growth

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Abstract
A model for leaf growth is constructed. The state of the leaf at any time is defined by eight variables; five of these define the ‘chemical’state of the leaf (labile carbohydrate, labile nitrogen, degradable structure, non-degradable structure and tissue water), the other three define its physical state (volume, area and thickness). The main assumption of the model is that the rate of synthesis of non-degradable structural material (cell walls) is a function of the rate of water uptake (and thence expansion) of the leaf tissues. The rate of water uptake is assumed to depend upon the amount of osmotically active solute in the leaf, and to be opposed by elastic and inelastic forces in the leaf tissues, which increase with leaf size. The model simulates a number of the observed features of leaf growth. For example, it qualitatively describes the observed changes in leaf thickness and rate of photosynthesis per unit leaf area with different growth light levels. The model can also be used to describe changes in metabolic activity during ontogenesis of a leaf.