Seed longevity and physical dormancy break of two endemic species of Dimorphandra from Brazilian biodiversity hotspots

Abstract

AbstractSeed longevity is dependent on seed traits and storage conditions. This study evaluated the seed longevity and physical dormancy (PY)-break of two species of Dimorphandra endemic to Brazilian biodiversity hotspots. Longevity was tested in situ, by burying seeds in their natural habitats (12 months), and ex situ, by storage in a cold chamber (5°C; 24 months). Seeds were taken at regular intervals to assess germinability at 30°C (12 h photoperiod) using intact and scarified seeds. Intact seeds (freshly collected, and after 12 months storage) were analysed using scanning electron microscopy. The germinability of freshly collected seeds of both species reached approximately 10% for intact seeds and >85% for scarified seeds. Cold storage maintained seed viability in both species, and broke dormancy for 35% of D. wilsonii seeds. After 12 months, only 55% (for D. exaltata) and 41% (for D. wilsonii) of the buried seeds were recovered; more than 90% of which remained viable in both species. Seeds gradually overcame PY during burial, with a higher germination increase for D. wilsonii (71%) than D. exaltata (32%). Dimorphandra exaltata seeds did not show clear structural changes after cold storage although D. wilsonii seeds evidently experience an increase in the depth of fracture lines. Burial promoted deep seed coat changes in both species, more intense in D. wilsonii, indicating that temperature and humidity variations throughout the year are among the main factors releasing Dimorphandra seeds from PY. The seeds of both studied species overcame PY during burial and are able to form small persistent soil seed banks.