Effects of short-term and prolonged saturation on seed germination of Amazonian floodplain forest species

Abstract

Many tropical floodplain species show enhanced germination after submergence in annual flood waters. In this study, we tested seed germination response to time in water (ranging 2–84d) among Amazonian floodplain species. To test seed response to short-term saturation, seeds from ten flood-tolerant woody species were air-dried or placed in water (i.e., saturated) for 45h before germination. Germination rates varied across species, achieving 50% germination in 12–58d among saturated seeds and 2–84d among air-dry seeds. Short-term saturation enhanced germination of the five shade-tolerant species by 14–100%. Three light-demanding species (Pseudobombax, Cordia, and Vitex) increased germination by 3–48% following air-drying. Cecropia and Laetia had poor germination in germination chambers (<20%), but Cecropia doubled germination rates in sunlit shade houses. Long-term saturation (removing seeds at 2-week intervals over 12 weeks) of four species showed that prolonged submergence enhanced germination only among Crataeva. The wind-dispersed Pseudobombax was intolerant of submergence >14d, while water-and fish-dispersed Crataeva seeds increased germination rates with submergence time, peaking at 6 weeks and maintaining >80% germination for up to 12 weeks. None of the ten flood-tolerant species required prolonged submergence for germination. Short-term saturation was sufficient to stimulate germination for most species, while prolonged submergence enhanced germination for one species, Crataeva. While species differed in seed physiology and seed size, they grouped into successional guilds of light-demanding species with dry-tolerant seeds and shade-tolerant species with recalcitrant seeds.