Storage Allocation in Seasonal Races of an Annual Plant: Optimal Versus Actual Allocation

This study uses optimal control theory to predict the conditions under which an annual plant's optimal schedule of carbon allocation should include allocation of storage at some point during the growing season. The optimal allocation schedule is defined as the schedule that maximizes final seed set. Storage of carbon, and later remobilization for allocation to reproduction, is an option in the model, and by providing the option, we ask whether storage of carbon is ever optimal for annuals. Predictions from the model are tested by comparing the observed differences in allocation between two seasonal ecotypes of a grassland forb with differences in the optimal behavior we predict for each. The model predicts that the autumnal ecotype should store carbon, while the vernal ecotype should not. These predictions qualitatively agree with the patterns, in the two ecotypes, of total nonstructural carbohydrate, which is our measure of storage. Analysis of the model indicates that the parameter responsible for the different predictions for the two ecotypes is the reproductive (seed mass) loss rate.