Seed Size Variation in Desmodium Paniculatum: II. Effects on Seedling Growth and Physiological Performance

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Abstract
(1) The effects of different environmental conditions on the growth and physiological performance of seedlings derived from different seed sizes were studied in the perennial herb Desmodium paniculatum. (2) The differences in seed weight are due to differences in the amounts of reserve substances. Seedings from larger seeds produce longer roots than those from smaller seeds and are able to emerge from greater depths of soil. (3) Seed size is positively correlated with cotyledon area and weight, leaf area, root weight and overall seedling dry weight. Seedlings from different-sized seeds have similar relative growth rates and patterns of dry-matter allocations and do not show differential response to shading. Seedlings from larger seeds respond to nutrient addition to a greater extent than those from smaller seeds. The contribution of epigeal cotyledons to the early growth of seedlings seems to depend more on their storage capacity than on their photosynthetic capacity. (4) Overall carbon gain and water-uptake capacity are proportional to seedling size. With reduced water availability, the advantage of seedlings from large and small seeds depends on whether they are grown singly or in competition. (5) Field experiments showed that seedlings from larger seeds were favored over those from smaller seeds during the early stages of growth in a drier, more disturbed, site. Seed size had no effect on relative survival in a forest habitat. (6) Variation in seed size, within the range of that produced by a single plant, results in seedlings differing significantly in size and physiological characteristics. Seedlings from larger seeds may have an advantage over those from smaller seeds if both types are grown in competition.

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