Document: GLE-3-37-16

Demography of Trachymene: Experimental seed cages.

WARDLE, G.M.*

The University of Sydney, Sydney, NSW, 2006, Australia ¹

Abstract:
The role of a soil seed bank in the demography of two Trachymene (Apiaceae) species from contrasting habitats was investigated. T. glaucifolia is an ephemeral annual that germinates following peaks in rainfall in a desert habitat. The perennial species T. incisa resprouts from a root stock after fire but also recruits from seed each year. T. incisa grows in sandy soils in coastal habitats which have frequent fires. Samples of sand were collected from 3 populations in the Simpson desert and were sieved. The number of seeds of T. glaucifolia varied spatially and temporally. There were significant interactions for month by population; population by dune position; and month by dune position. Depth was not significant indicating that seed is present down to 3cm. The fate of dispersed seeds, either by germinating, surviving in the sand, seed predation or death was determined by sowing seeds of known age into a series of nylon seed cages. The experimental treatments were 1) open cages, no added seed, 2) open cages +50 seeds 3) closed cages + 50 seeds, and 4) procedural control for closed cages - covered but open at the sides. Seed emergence showed a significant cage treatment by dune position interaction. Fewer seeds emerged in cages located in the swale compared to the side and top of the dune. Seed gains and losses were minimal. Fresh seed of T. incisa was sown into experimental seed cages with the following treatments: burn vs. nonburnt vegetation; 3 planting dates and 3 densities (25, 50, 100 seeds). ANOVA on emergence indicated that the first week of planting exhibited significantly higher emergence. There was no effect of burn history or density on the mean number of seeds emerging per cage. The estimates of germination percentages and carryover in the seed bank will be used to model the population dynamics of these plants in variable environments.

Keywords: Seed bank, emergence, desert, rainfall

This abstract is being presented at: 10:30 AM in session:
PLANT DEMOGRAPHY