Optimal level of chemical defense decreasing with leaf age
We study the optimal level of defense chemicals contained in a leaf as a function of leaf age. The assumptions are as follows. The loss of leaves due to herbivory decreases with the defense chemical concentration, indicating the protecting effect of the chemical. The daily net photosynthesis of a leaf decreases with its age. Using newly acquired photosynthetic products, the plant produces new leaves that may contain defense chemicals. The defense chemical contained in old leaves may also be reallocated to new leaves. To make the argument simple, we here consider a plant in a vegetative phase growing exponentially in a constant environment, constantly producing new leaves. We examine the optimal age-specific pattern of defense chemical in leaves that realize the maximum growth rate of leaves. This optimality criterion is supported by the result of \textit{Y. Iwasa} and \textit{J. Roughgarden} [ibid. 25, 78-105 (1984; Zbl 0531.92002)], who demonstrated, using a dynamic optimization model including multiple vegetative organs and reproductive activity, that the optimal balance between different parts of a vegetatively growing plant is in fact given by the one that achieves the fastest growth rate of the individual.
optimal age-specific pattern of defense chemical in leaves
scientific article; zbMATH DE number 954534