Ecophysiology and morphology of seed germination of the neotropical lowland tree Genipa americana (Rubiaceae)

摘要

Genipa americana is a semi-deciduous tree species widely distributed in neotropical forests prone to flooding, from Mexico to northern Argentina. The morphology of G. americana seeds and their post-seminal development were studied, and germination response investigated in relation to storage in water, substrate water volume, osmotic potential and temperature and light regimes. The seeds are flattened and seedlings are phaneroepigeal with leafy cotyledons. Seeds stored in water retained viability for up to 6 months, but germination and seedling emergence were reduced after 4 months. Germination was not affected under waterlogged conditions, but seedling emergence was reduced at a water volume corresponding to a water column 2X deeper than the seedsmean thickness (70 ml). When seeds were osmotically stressed, a reduction in the rate and germination percentage occurred at -0.2 MPa and germination was drastically inhibited at -0.6 MPa. Seeds germinated over a wide range of temperatures (15-40deg C), with an optimum at continuous temperatures of 25 and 30deg C. Light was not required for germination, and no dormancy mechanisms were observed. The seed and seedling morphology and the germinative responses of the species may permit its regeneration in periodically flooded lowland forests and riparian habitats, and are probably key factors in explaining the wide distribution of the species.