Germination of small-seeded tropical rain forest plants exposed to different spectral compositions

Abstract

Seeds of 11 very small-seeded species with different degrees of shade tolerance as juveniles were tested for their response to neutral shade (6% daylight), green shade (3%), and darkness. Germination was monitored over 46 weeks. All species germinated in daylight to some extent. Species of Pternandra and Urophyllum, commonly found as juveniles in deep shade, germinated to the same percentage in green shade as in daylight, although over a longer time period, and to a lower percentage in the dark. Percentage germination of Gynotroches axillaris and Pellacalyx saccardianus, also found as juveniles in deep shade, was similar in all treatments, but much faster in daylight. Species of Ficus, which are found commonly as seedlings in deep shade but require higher irradiance for onward growth, germinated rapidly in daylight, and to a lower percentage and after a longer time in green shade than in the dark. Melastoma, which establishes in large gaps, germinated only in daylight. As most species can germinate under a spectral composition similar to canopy shade it is likely that they can germinate under a closed canopy in nature and may become established without the formation of even a transient canopy gap provided leaf litter is absent. Keywords: germination, red/far-red ratio, shade tolerance, tropical rain forest.