VARIATION AMONG POPULATIONS OF PRUNELLA-VULGARIS L IN PLASTIC RESPONSES TO LIGHT

Phenotypic responses to photon flux density (PFD) by five populations of the herbaceous perennial Prunella vulgaris L. were compared. Plants from each population were grown in two light environments, and we measured the effect of PFD on overall performance (size) as well as the responses of several physiological traits to PFD. Both measures of size and physiological traits differed significantly between light environments and among populations. Significant population-by-environment interaction was detected for measures of size but not for any physiological traits. These results indicate significant differences among populations in the extent to which size is reduced by a decrease in PFD. However, these differences are not the result of variation in the responses of the physiological traits we measured. A comparison of the patterns of correlations among traits in the two light environments indicated signficant similarity of correlation structure between environments. This result contrasts with those of studies showing strong environmental dependence of phenotypic relationships between traits.