Anthropogenic stress and natural selection: variability in radish biomass accumulation increases with increasing SO₂ dose

Although there is a strong relationship between genetically based variability of a given character and the potential for natural selection to act on that character, most studies of the effects of environmental factors on plants examine the mean responses of plants in a population and not the variability among plants in the population. Yet variability in the response among individuals to an environmental stress could foretell changes in a population that might not be evident from examination of mean responses. Here we report an analysis of data from several experiments on radish plants showing a significant relationship between the coefficient of variation for biomass production by radish plants and the concentration of SO at which these plants were fumigated. Increased variability as a result of SO exposure may have been due to genotypic differences in SO resistance among plants, suggesting a route by which the rapid selection of SO resistant plant populations may occur in habitats characterized by severe SO stress. Increased variability may have also been due to the effect of SO on processes controlling phenotypic plasticity of radish growth. Since SO affected variability without necessarily affecting mean plant growth, these results also show that examination of variability in the responses of plants to stresses may be equally or more biologically meaningful than sole examination of mean responses. Furthermore, these results show that care must be taken when constructing parametrically derived dose–response models for predicting the effect of SO on plants. If it is common for SO to increase the amount of variation in plant populations, then parametric statistical functions would be an inappropriate tool for predicting the effect of SO on plants.

Duke Scholars

Author William E. Winner DKU Faculty