Seedling dynamics, relative to later life stages, play a disproportionate role in determining the species composition in tropical forests. Species performance differences are often linked to differences in life history strategy, approximated by measures of the functional traits by which species acquire resources and defend against enemies. Although adult trees differ in eventual canopy position or habitat preferences, their seedlings often germinate into a comparatively homogenous environment -- the dark understory where acquisition of light is difficult and agents of mortality plentiful. Most research to date has quantified maternal investment in seed mass as a proxy for potential species differences at the seedling stage. Seed mass alone, which varies over several orders of magnitude even within the same family, may not predict well how those young individuals respond to environmental stresses. Instead, survival in the first year reflects differences among species in tissue construction and ability to acquire resources in the dark understory. We measured multiple leaf, stem, and seed traits on seedlings from over 125 woody tropical species in Yasuní National Park, a highly diverse Amazonian forest in eastern Ecuador, to understand relationships among seed mass, resources acquisition traits and 15 years of seedling survival and performance.
Results/Conclusions
Leaf, cotyledon, stem, and root traits measured in newly field-germinated seedlings at the point of full emergence of the first photosynthetic organ varied widely among species. Seed mass, representing the trade-off in maternal investment between seed number and size, tended to correlate with cotyledon type and leaf or stem tissue density. Larger seeds were more likely to have storage-type cotyledons rather than photosynthetic cotyledons, and invested in thicker leaves and stems using those reserves. However, there was significant variation in seed mass within each cotyledon type, and storage vs. reserve cotyledon type was an important predictor of both a coordinated suite of resource acquisition traits and trade-offs in growth and survival in the first year of a seedling’s life. Traits that confer success at the seedling stage, where species encounter a different environment than they do as adults, may not be the same as those that confer success at later life stages. Understanding how trait differences contribute to the maintenance of diversity in a highly diverse tropical forest requires integrating performance and relevant traits across different life stages, especially the traits that predict performance at the highly dynamic seedling stage.