Seed hydration memory in the invasive alien species Leucaena leucocephala (Lam.) de Wit (Fabaceae) in the Caatinga

Seed hydration memory is an adaptive strategy for plants in semiarid environments where water availability is irregular and unpredictable. Species native to these environments that have memory benefit from discontinuous hydration during their germination process and acquire tolerance to environmental stresses. The guiding question of this study is "does an alien species that invades a semiarid ecosystem also have seed hydration memory and benefit from discontinuous hydration?" To answer this question, we collected seeds of Leucaena leucocephala (Lam.) de Wit, an alien species that invades a Brazilian Tropical Dry Forest. We subjected the seeds to 0, 1, 2 and 3 hydration/dehydration cycles (HD cycles) at three different time intervals and, subsequently, to water, saline and thermal stresses. In addition, we used modeling to define the osmotic and thermal limits for occurrence of L. leucocephala and evaluated whether these limits increase after discontinuous hydration of seeds. The cycles of HD positively influenced the germination of seeds submitted to all stresses evaluated, increasing seed tolerance to treatments of water, saline, and thermal stresses. Discontinuous hydration increased the osmotic limits of salinity and thermal tolerance, although not increasing the osmotic limit of water deficit. Our results show that HD cycles also change the patterns of germinative responses of an invasive species to the environmental stresses of the invaded ecosystem.