PHENOTYPIC PLASTICITY IN POLYGONUM PERSICARIA. II. NORMS OF REACTION TO SOIL MOISTURE AND THE MAINTENANCE OF GENETIC DIVERSITY.

Adaptive phenotypic plasticity is the predicted evolutionary response to fine-grained fluctuation in major environmental factors, such as soil moisture in plant habitats. This study examines genotypes from two natural populations of Polygonum persicaria, one from a relatively homogeneous, moderately moist site, and one from a site in which severe drought and root flooding occur within single growth seasons. Norms of reaction (phenotypic response curves) were determined for a random sample of eight and ten cloned genotypes, respectively, from each of the populations over a controlled moisture gradient ranging from drought to flooding.