AN INTERPRETATION OF PHENOTYPIC PLASTICITY IN AGROPYRON REPENS (GRAMINAE)

Phenotypic plasticity and genotypic variation were studied in Agropyron repens L. (Beauv.) collected from populations in two grassland communities which differed in the length of time since the last major disturbance. Twenty genotypes were collected from each population. Each genotype was vegetatively propagated, and subjected to six different treatments in a greenhouse. Phenotypic plasticity and genotypic variability were measured as across- and within-treatment standardized variances respectively. Patterns of plasticity were measured by genotype correlations across treatments. The results were presented graphically by the regression method of Garbutt and Zangerl (1983). Analysis of variance revealed significant population, genotype and treatment effects. Significant positive correlations between magnitude and variability of performance were found for all characters. Phenotypic plasticity and magnitude of performance were generally greater in plants collected from the older established field. Evidence for greater specialization in the older population was suggested by negative correlations between performance in the most favorable and least favorable treatments and by greater dissimilarity of genotype response across treatments. A more variable phenotypic response across treatments (i.e., higher plasticity) for plants from the older population may therefore be a consequence of specialization and not an adaptive trait per se.