Seed germination of Acacia dealbata and Acacia mearnsii
Acacia dealbata (Fabaceae: EPPO List of Invasive Alien plants) and A. mearnsii are both native to Australia and are invasive in Africa, Asia, the Americas, the EPPO region and New Zealand. In the EPPO region, both species are invasive in coastal and riparian Mediterranean habitats. Seed biology, ecology, seedbank density, and seed longevity are important drivers of plants’ competitive performance, contributing to the invasion success. Invasive plant species with persistent soil seedbanks are particularly difficult to manage as, even after mature individuals are removed, seeds remain in the soil. Mature pods of A. dealbata and A. mearnsii were collected from six locations in the Mediterranean region, three from France, two from Italy and one from Portugal. All seeds were stored under controlled conditions for a period of 2 weeks and non-scarified seeds were sown on a 1 % water agar substrate in Petri-dishes and incubated in a growth chamber at 15, 20, and 25oC, in light (12 h light per day). Scarified seeds, where the seed coats were manually chipped with a scalpel were incubated in growth chambers with constant temperature and light (5, 10, 15, 20, and 25oC) (12 h of light per day). Both species showed a higher germination capacity at 25oC in non-scarified seeds; A. dealbata reached a germination maximum of 55 %, while A. mearnsii reached 40 %. Scarified seeds of both species reached germination percentages >95 % at all temperatures except at 5oC in dark conditions. Scarification was important to break dormancy and promote germination. The study confirms that A. dealbata and A. mearnsii have physical dormancy, a trait that promotes the establishment of a persistent soil seed bank. Seeds are highly dependent on scarification for germination, an adaptation that allows the seeds to germinate when conditions are more suitable, promoting the survival of seedlings in nature.
Sources
Dessì L, Podda L, Brundu G, Lozano V, Carrouée A, Marchante E, Marchante H, Petit Y, Porceddu M, Bacchetta G (2021) Seed germination ecophysiology of Acacia dealbata Link and Acacia mearnsii De Wild.: Two invasive species in the Mediterranean Basin. Sustainability 13, 11588.