Germination of tropical legume seeds from Brazilian seasonally dry environments: effects of alternating temperature and water stress

Legumes dominate many tropical landscapes, often producing water-impermeable seeds (physical dormancy, PY). The present study evaluated (1) whether an alternating temperature regime (AT; 20–40 °C) enhance germination, mainly by promoting PY-break, and (2) the effect of reduced water potentials ( Ψ = 0.0, −0.4, −0.8, −1.2 MPa) on germination of legumes from Brazilian seasonally dry environments. Experiment 1 involved all six study species, which differed in the fractions of nondormant (ND) and PY seeds, comparing a constant room temperature (CT, 25 °C; 30 days) with a 2-week AT followed by other 2 weeks of constant conditions. Experiment 2 tested four species (ND or with only a fraction of PY) under water stress (for 30 days), followed by stress relief and monitoring of germination recovery for 15 additional days. AT did not enhance germination, but seeds mostly maintained their viability. Water stress strongly inhibited the germination of ND seed fractions, with post-stress germination recovery ranging from 18% to 49%. Mimosa caesalpiniifolia Benth. was an exception, showing high seed mortality. Overall, legume seeds may persist by withstanding thermal and hydric stress, enabling recruitment under more favorable conditions. Such strategies likely contribute to regeneration in tropical seasonal environments, increasingly affected by warming and aridity due to climate change.