The effect of salinity on different developmental stages of an endemic annual plant, Aster laurentianus (Asteraceae)

Salinity reduces substrate water potential, thereby restricting water and n utrient uptake by plants: salinity may also cause ionic imbalance and toxic ity. Because substrate salinity fluctuates through the growing season, a pl ant may be exposed to different salinity levels, at various stages of devel opment, with potentially significant consequences on population dynamics. H ere, we present the results of a study of the effect of substrate salinity on seed germination, seedling emergence, and growth of Aster laurentianus, an annual marsh plant, endemic to the Gulf of St. Lawrence and potentially threatened. Seed germination was reduced in low salt concentration (10 g se a salt/L) and completely inhibited by salinity levels greater than or equal to 20 g sea salt/L. However, this inhibiting effect was reversible: seeds from the salt treatments germinated readily after being washed in distilled water. Though seedling emergence was diminished at low salinity levels, po stemergence survival was little affected. Plant growth was reduced, but net carbon assimilation rate was not affected by high salinity levels. Increas ed root respiration and respiratory costs associated with salt tolerance mi ght have contributed to lower C accumulation at higher salinity levels. All developmental processes considered are thus negatively affected by substra te salinity, with potentially significant consequences on population abunda nce and distribution in salt marshes. Yet, the tolerance of this species to high salinity levels after seedling emergence is remarkable. Seed germinat ion represents a major bottleneck in the species life cycle, potentially co ntrolling local distribution and abundance in the natural habitat.