Seed-seedling allometry in tropical rain forest trees: seed mass-related patterns of resource allocation and the reserve effect.

Abstract

1. The seedlings of larger seeded species generally perform better than those of smaller seeded species under a variety of hazards. The reserve effect proposes that larger seeded species retain a greater proportion of their initial seed resources and their seedlings are therefore better provisioned to cope with post-deployment resource deficits. 2. This hypothesis was tested with a suite of 32 Australian rain forest species with storage cotyledons, and seed reserve mass ranging from 36 mg to 25 g. Seedlings germinated in dim light were harvested as their first set of leaves became fully expanded, dissected into shoot, root and left-over cotyledons, dried and weighed. 3. In cross-species, allometric analyses, the mean mass of the shoot-plus-root scaled less than proportionately (slope c. 0.8), and mean cotyledon mass more than proportionately (slope c. 1.1) with either initial seed mass or seedling mass. These slopes were significantly different from each other. Both conditions for a reserve effect were therefore fulfilled. Cotyledons ranged from 45% of total seedling mass in the smallest species, to 92% in the largest. 4. Solid evidence for a reserve effect was detected within two of four families tested (Lauraceae and Myrtaceae), but only in 7 of the 22 species for which there were sufficient data. 5. Even if the reserve effect has present day utility for enhanced seedling performance in larger seeded species, it may have evolved in response to selection for a greater relative retention of initial seed mass during seedling deployment in larger seeded species, combined with selection for greater deployment of seed reserves to the initial shoot and root of smaller seeded species.