Humidity and temperature interact in breaking physical dormancy in Fabaceae seeds from the Brazilian semiarid region.

PREMISE: In semiarid ecosystems such as the Brazilian Caatinga, physical seed dormancy (PY) is critical for plant persistence when water is unpredictable, but how soil moisture and temperature regulate PY release and seed longevity in species of native Fabaceae that have different growth forms is unknown.

METHODS

Seeds of the herbaceous species Centrosema pascuorum and Crotalaria retusa and tree species Mimosa ophthalmocentra, M. tenuiflora, and Piptadenia retusa were collected in the Caatinga and tested in the field and laboratory to assess dormancy, viability, and germination. Seeds were either buried at the collection site and periodically exhumed over 15 months, or stored dry or with wet-dry cycles at constant or fluctuating temperatures.

RESULTS

Seeds of herbaceous species had rapid PY release and seed depletion shortly after the onset of rainfall, leading to synchronized seedling emergence. Seeds of the trees M. ophthalmocentra and M. tenuiflora maintained high dormancy and viability, indicating strong potential for persistent soil seed banks, whereas seeds of Piptadenia retusa had low persistence due to rapid dormancy loss and high mortality. Across species, PY release was maximized under wet-dry cycles at high temperatures, revealing a synergistic effect of moisture pulses and heat.

CONCLUSIONS

Temperature-moisture interactions characteristic of the Caatinga control PY release and seed persistence, with growth form shaping contrasting regeneration strategies. The delayed release of PY in trees spreads germination over time, enhancing persistence under unpredictable rainfall. Early PY release in herbs optimizes exploitation of short favorable windows to complete their rapid life cycle.