Effects of Seed Size and Growth Form on Seedling Establishment of Six Monocarpic Perennial Plants

Abstract

(1) Effects of seed size and seedling morphology on the establishment of six monocarpic perennials were examined in glasshouse experiments. Both withinand between-species comparisons of seed-size effects were made as seed weight varied by more than two orders of magnitude among species and by 3 to 20-fold within a species. Experiments were conducted in four ground-cover types: bare soil, litter cover, vegetated, and vegetated plus litter. (2) In vegetated cover, emergence of the two small-seeded species, Verbascum thapsus and Oenothera biennis, was significantly lower than in litter and bare soil. In contrast, emergence of the medium (Dacus carota and Dipsacus sylvestris) and large-seeded species (Tragopogon dubius and Arctium minus), was not significantly reduced in the presence of vegetation. Although the rate of emergence of all six species was significantly reduced in vegetated cover, there were no between species differences in seedling emergence rates in any cover type. (3) Relative growth rates of all six species were significantly lower in vegetated cover compared with litter and bare soil and the effect was greatest on the small-seeded species. At the end of the experiment, seedling weight in vegetated cover was positively correlated with seed weight. In non-competitive cover types (litter and bare soil), seedling weight was independent of initial seed weight. (4) Relative growth rates of seedlings in non-competitive cover types were inversely related to seed size. In bare soil and litter, the small-seeded species had relative growth rates twice those of the large-seeded species. In vegetated cover this pattern was reversed; the species with large seeds had the highest relative growth rates. (5) The growth form of a seedling did not have any effect on its probability of establishment in any cover type. Species with different growth forms and similar seed sizes had equal emergence, survival, and relative growth rates in all four cover types. (6) Within species differences in seed size had a significant effect on seedling growth in non-competitive cover, but had no effect on seedling growth in competitive cover. Thus, both withinand between-species differences in seed size had similar effects on seedling establishment success in different types of ground cover.