title: A mixed strategy in the annual endemic Aster laurentianus (Asteraceae)--a stress-tolerant, yet opportunistic species.
abstract: Several environmental factors influence the distribution of plants in coastal salt marshes. Substrate salinity is among the major factors preventing several species from establishing near the water line. However, interspecific competition for light and nutrients is often significant in determining the upper limit of plants along the salt marsh gradient. In this study, we tested the effects of substrate salinity and light and nutrient availability on the performance of the annual Aster laurentianus (Asteraceae), an endangered species of eastern Canadian salt marshes. This species is typically found in a narrow band along the shores of shallow lagoons, cornered between the high water line and the dense, herbaceous community of the upper marsh. Low light availability was the most significant factor limiting plant performance. Salinity had little effect on A. laurentianus as, unexpectedly, did nutrient availability. Yet plants were able to absorb nutrients when these were made more available. Luxury consumption, the uptake of excess nutrients, may make sense for this annual plant because the habitat in which it grows is subject to frequent disturbances (e.g., sand accretion and salinity pulses) that may kill canopy species and release suppressed A. laurentianus individuals. These results suggest that interspecific competition for light may play a significant role in restraining A. laurentianus from the upper part of salt marshes. Luxury consumption may help the species to opportunistically take advantage of release from taller species, particularly towards the upper edge of the salt marsh gradient.
authors.affiliation: Département de biologie, Université Laval, Sainte-Foy, Québec G1K 7P4, Canada.
authors.forename: Gilles
authors.initials: G
authors.lastname: Houle
authors.forename: Sébastien
authors.initials: S
authors.lastname: Valéry