Habitat Productivity and Optimal Growth Schedule of Annual Plants in Seasonal Environments

An optimal-allocation model was developed for annual plants in a seasonal environment. The model predicts that the graded allocation strategy is optimal in habitats with a low productivity, while the bang-bang control strategy is optimal in habitats with a high productivity. This dichotomy is caused by the difference in the optimal vegetative size, Vopt, that maximizes instantaneous net photosynthates. This Vopt changes with the seasonal changes in resource availability, for example, irradiance, day length and temperature, in the habitats. In the low productivity habitats, Vopt is small, and plants can reach it, which increases as the environmental factors become favorable. After reaching Vopt , they allocate resources to their vegetative parts in order to keep increasing Vopt, and allocate the remaining resources to their reproductive parts. In the high productivity habitats, Vopt is large and plants cannot reach it before it does not pay them to keep Vopt. The plants completely switch their growth from purely vegetative to purely reproductive. In both habitats, plants recover resources from their vegetative parts late in their growing period in order to keep Vopt, because Vopt decreases as the environmental factors become unfavorable, and reallocate these resources to their reproductive parts. The model also predicts that plants with a larger initial vegetative size (i.e. larger seed size) should begin their growth later.