The ecological significance of plasticity.

Plastic responses of plants to environmental factors may be placed in an ecological context by regarding them as components of sets of traits which are predictably related to habitat stability and productivity. In ephemeral plants of temporary habitats plasticity is a major component of the mechanisms which tend to sustain reproduction when these plants are exposed to stress. When perennials of more stable habitats are subjected to stress the most frequently observed effect of plastic changes in allocation is to defer reproduction, a mechanism which appears to safeguard survival of the parent plant. It is suggested that plasticity is of vital importance in resource acquisition by plants. This hypothesis is supported by the results of experiments in which the roots and shoots of plants of contrasted ecology have been subjected to controlled patchiness in resource supply. We conclude that in plants of productive habitats high morphological plasticity is part of the foraging mechanisms which project new leaves and roots into the resource-rich zones of the constantly changing environmental mosaic created by the activity of competing plants. In long-lived plants of chronically unproductive habitats plasticity is expressed primarily through reversible physiological changes. These appear to maintain the viability and functional efficiency of leaves and roots over their long life spans and facilitate exploitation of the pulses of temporary and unpredictable resource supply which are characteristic of unproductive habitats.