GENOTYPIC AND PLASTIC VARIATION IN PLANT SIZE - EFFECTS ON FECUNDITY AND ALLOCATION PATTERNS IN LYCHNIS-FLOS-CUCULI ALONG A GRADIENT OF NATURAL SOIL FERTILITY

1 Genotypic and plastic variation in plant size, and trade-offs among components of reproduction were studied using cloned individuals from 24 parental plants of the perennial hay-meadow species Lychnis-flos-cuculi, planted in four sites along a gradient of natural soil fertility. 2 Plant biomass, survival and fecundity differed significantly among clones and sites. Differences in survival and early components of fecundity among clones were strongly average rosette biomass attained during the first year. 3 There were significant clone-site interactions. However, a small number of clones which ranked high for plant biomass and fruit production at all sites, made a large contribution to local fruit production within a year across the entire gradient. 4 Patterns of biomass allocation and timing of first reproduction differed significantly among clones. A large part of this variation could be explained by clonal differences in average plant biomass attained during the first year. We conclude therefore that clonal variation in allocation patterns reflected differences in resource acquisition, rather than differences in partitioning strategies underlying life-history evolution. 5 Consequences of delaying first reproduction varied among sites. Precocity was favoured in the least productive site, whereas at intermediate soil fertility individuals that postponed reproduction gained a three-fold increase in fecundity at first reproduction, with no significant reduction in survival to this stage. Optimal timing of reproduction may thus vary at a small scale. 6 Genetically based trade-offs between only observed in the less productive sites. Costs of reproduction were also only apparent at such sites, supporting the idea that the expression of trade-offs and costs is most likely under low resource conditions. 7 In the more productive sites, within- and among-clone correlations between etative and generative reproduction, and among five components of fecundity were generally insignificant or positive. This available, differences in both microsite quality and resource a governed patterns of covariance. 8 Fruit predation by caterpillars of the noctuid Hadena bicruris was dependant on plant size. In the site with lowest individual fecundity, conferring a relative advantage to smaller sized individuals.