Seedling morphology of non-pioneer trees in Central Amazonian várzea floodplain forests

The relation between seed size, seedling morphology and germination is analyzed for 11 non-pioneer tree species typical of Amazonian várzea floodplain forests. A classification of seedling morphology and establishment strategies is presented. Seeds were collected in the field (várzea), put into plastic bags and transported to the INPA (Amazon Research Centre, Manaus, Brazil) where they were planted under semi-natural conditions. The seedlings were classified according to seed weight and size (length x width) and the position and function of their cotyledons. Four main types of seedlings were found: cryptocotylar hypogeal with reserve or absorption cotyledons (CHR), phanerocotylar epigeal with foliaceous (photosynthetic) cotyledons (PEF), phanerocotylar epigeal with reserve cotyledons (PER), and phanerocotylar hypogeal with reserve cotyledons (PHR). The most frequent seedling type was PEF (followed by CHR, PHR, and PER), which also had the smallest seeds and the highest germination percentages. Small seeds germinated earlier, also within a germination type. Although 11 tree species represent only a very small percentage of the species occurring, some trends can be shown which perhaps are found also in other trees of the várzea forest. It may be expected that the dominance of PEF seedlings in várzea is not a coincidence: in the nutrient-rich várzea environment the presence of nutrient-supplying cotyledons is not as important as in nutrient-poor environments. A newly established seedling can get nutrients from the soil, and foliaceous photosynthetic cotyledons are sufficient for fast initial growth. Nevertheless, taken together the species with reserve cotyledons accounted for almost 64 % of the analyzed species. These reserve cotyledons enhance fast growth in an environment with extreme flooding conditions and thus with a reduced period of favorable conditions for establishment