Environmental control of seed dormancy and germination of Mimosa calodendron (Fabaceae): implications for ecological restoration of a highly threatened environment

Abstract

Rupestrian grasslands over ironstone outcrop, locally named canga, are montane ecosystems with restricted distribution known to harbor an unusually a large number of endemic plant species. These communities are highly threatened due to their high sensitivity to habitat conversions and extreme low resilience derived from anthropogenic pressure. Ecological restoration attempts on degraded rupestrian grassland areas have not yet been successful. Mimosa calodendron is an endemic canga shrub thought to play a facilitator role and, therefore, may enhance seedling recruitment in degraded areas. Since dormancy and slow germination are key factors of the biology of seeds and may hamper their use in ecological restoration, this study aimed to investigate the environmental control of seed dormancy and germination of M. calodendron seeds. We tested the effect of mechanical scarification, light and different incubation temperatures on seed germination. The effect of scarification on water uptake by seeds was also measured. M. calodendron seeds have physical dormancy and scarification was an effective treatment to promote high and rapid germination. Heat treatment also increased germination percentage of non-scarified seeds, but was less efficient than scarification. Once water uptake occurred, germination took place under a broad thermal gradient, regardless of light condition. Therefore, the germination profile of M. calodendron seems to be suitable for uncomplicated use in restoration projects, requiring only a pretreatment for dormancy release.