Seed size effects and competitive ability in Thlaspi arvense L. (Brassicaceae)

Abstract

We examined the effects of seed size on plant size and competitive ability of Thlaspi arvense L. grown with and without intraspecific competition under contrasting soil fertility regimes. For solitary plants from each of four half-sibship families, seed mass was positively correlated with percentage germination, cotyledon size, and plant biomass after 15 d of growth, but differences in plant biomass largely disappeared at later dates. Small and large seeds of a single maternal family were sown in uniform or mixed arrangements of seed size classes (small:large; 100%:0%; 75%:25%; 50%:50%; 25%:75%; 0%:100%) at each of two densities (8 or 16 seeds·pot–1) under low and high soil nutrient regimes. In mixtures at low density under low soil fertility, plants from small seeds had significantly lower relative yields than expected. At high density, under either low or high nutrient conditions, plants from large seeds had significantly greater relative yields than expected. Hence, under most conditions, size inequalities between plants from seeds of different size resulted in a relative competitive advantage for plants from large seeds. The duration and extent of differences in plant size arising from T. arvense seeds of contrasting size depends on maternal genetic differences, intensity of intraspecific competition, and soil fertility.