SULTAN, S.E.: Phenotypic Plasticity and Ecological Breadth in Plants

Plants show dramatic phenotypic plasticity in response to different environmental circumstances. These environmental responses generally include reductions in growth when resources are limited. However, phenotypic responses to different environments may also include developmental changes in ecologically important traits that serve to offset external resource limits. The capacity for such functionally adaptive plasticity may help shape the range of environments species successfully inhabit in nature. Hence, differences among species in patterns of developmental plasticity may have important ecological implications. Comparative studies of four species in the genus Polygonum provide a case study illustrating the relation of individual plasticity to ecological breadth. In a series of greenhouse and growth chamber experiments, replicates of inbred lines sampled from natural populations of the four species were raised at contrasting light, moisture, and nutrient levels. Results show the species differ in plasticity for several developmental traits critical to resource use, including biomass allocation to different organs, leaf size and structure, root morphology and spatial deployment, and root extension rates. They also differ in a more complex aspect of plasticity: environmental responses expressed in the offspring. These “cross-generational” effects were found to include not only changes in seed size but specific changes to seedling development and morphology. Differences in both functional and cross-generational aspects of adaptive plasticity correspond to differences in the range of environments the Polygonum species inhabit in nature. Knowing patterns of individual developmental plasticity informs our understanding of ecological distribution, including the nature of narrow “specialist” versus widespread “generalist” species.