Seed demography of Ambrosia artemisiifolia
Ambrosia artemisiifolia (Asteraceae, EPPO list of invasive alien plants) is an annual that originates from North America. It is a weed that colonizes both spring crops and disturbed habitats. Its pollen is an important allergen, threatening human health. The demography of A. artemisiifolia is studied here, in order to better understand its invasive processes. The plant produces large numbers of dormant seeds in autumn able to survive for up to 40 years in soil. A portion of the seeds germinate in spring, while the rest of the seeds enter secondary dormancy.
In 2005-2006 eight French populations were studied from a range of locations and habitats. For each population, the size of the soil seed bank, plant densities, seed rain (seeds falling from plants), and the effects of soil disturbance on seed germination were analyzed.
The total soil seed bank (recorded to a depth of 20 cm) ranged from 250 to 5000 seeds/m2. The top 5 cm of soil held more seeds (200 to 2800 seeds/m2) than deeper layers. Large differences in seed density between sites were mostly explained by the type of habitat (differences in soil perturbation, competition, etc). There was large variation by site in the proportion of the seed bank that germinated in spring. The seed rain at the end of the plant growing season ranged from 500 to 7300 seeds/m2, correlating significantly to both plant volume and density per m2. Disturbance of the top layer of soil greatly increased germination rates in closed habitats such as fallow land but decreased rates in open wasteland habitats characterized by low densities of other plant species. These results suggest that the invasion potential of A. artemisiifolia is closely related to its persistent soil seed bank and how this is affected by processes in different habitats.
Sources
Fumanal B, Gaudot I, Meiss H, Bretagnolle F (2006) Seed demography of the invasive weed: Ambrosia artemisiifolia L. In: Neobiota. From Ecology to Conservation. 4th European Conference on Biological Invasions. Vienna (Austria), 2006-09-27/29, BfN-Skripten 184: page 127 (abst.).
Neobiota website: http://www.umweltbundesamt.at/neobiota