Overcoming germination barriers in four native Malvaceae shrub species of Reunion island to improve restoration in arid habitats

Abstract

Islands are well-known to house an incredible biodiversity, higher level of threatened species and extinctions than mainlands. Because of human activities and climate change, these endangered regions required advanced conservation and restoration strategies.In this study, we investigated seed germination ecology of four native Malvaceae species (Dombeya acutangula, Dombeya populnea, Ruizia cordata and Thespesia populneoides) of degraded dry lowlands of Reunion Island. We measured seed imbibition, investigated the dormancy class of seeds, determined light requirements for germination and identified treatments to improve germination of these species. For this purpose, germination tests were performed over 32 days and two photoperiods (12 h/12 h or 0 h/24 h), by using seeds treated with H2O2, gibberellic acid and smoke water. Mechanical and chemical scarifications as well as heat treatment were also carried out. Germination percentages were analyzed by fitting generalized linear models (GLMs) with a logit link function.For the four species, a significant mass increase is detected for scarified seeds after a week imbibition (>60% mass increase). Germination percentages of seeds treated with H2O2, GA3 and smoke water were not significantly different from control seed. On the contrary, scarified seeds exhibited significantly higher germination percentages than control seeds. In addition, germination speed was also significantly higher for scarified seeds. These results are congruent with a physical dormancy phenomenon of seeds of the four Malvaceae shrubs. In addition, no particular light requirement was observed for germination. Artificial methods to break dormancy and stimulate germination described in this study could improve establishment success in arid habitats.