Seedling longevity under deep shade in relation to seed size

1 Seedlings were grown in dense shade, below the compensation point. At cotyledon stage (i.e. when placed in dense shade from germination onwards), species with larger seed mass tended to survive longer. This was true within 11 phylogenetically independent contrast (PIC) pairs of plant species, as well as across all 22 species. 2 RGR of early seedlings in full light (to day 10 after germination), and cotyledon dark respiration, were measured as potential indicators of the speed with which metabolic resources in the seed were used during early seedling development. These indicators proved not to be such good predictors of longevity under dense shade as was seed mass itself. 3 Seedlings were also grown in the light until live days after true leaves appeared, before being transferred to dense shade. The different behaviour of these true-leaf seedlings was consistent with the idea that extra resources in seeds are the direct cause of longer dense-shade survival. Longevity in dense shade at leaf stage was often shorter than for cotyledon-stage seedlings, especially for larger-seeded species. Longevity in dense shade at leaf stage was best correlated with a slow potential RGR in full light measured over days 10 30 of growth. Correlation with seed mass was marginal and probably an indirect correlation via RGR, and there was no correlation with leaf dark respiration.