Within-population genetic diversity of Taraxacum officinale (Asteraceae): differential genotype response and effect on interspecific competition.

Clonal offspring of five morphologically distinct individuals of Taraxacum officinale were planted in a greenhouse experiment with each of three competitors, Plantago major, Poa pratensis and Trifolium pratense. The competitors were chosen to represent a series of competitive environments experienced by a natural population of T. officinale through the year. Differences in size, morphology, and response to the competitive environments were found among clones and support classification of the five individuals as distinct genotypes. Both differential competitive responses (alteration in performance) and competitive effects (impediment by competitor performance) were exhibited among genotypes. The differential response by the T. officinale genotypes to the competitors indicates that the biotic environment may influence the genetic structure of a population. The biotic environment in this case is determined by the sequential appearance and dominance of competitors in a field rather than the spatial distribution of these competitors. Since competitors change in relative dominance across seasons, competition is likely to be a component of the genotype by season interaction that had been observed in the natural population. Thus, differential responses among genotypes to a temporally and spatially fluctuating biotic environment may contribute to the maintenance of within-population genetic diversity.