The effects of drought and waterlogging conditions on the performance of an endemic annual plant, Aster laurentianus

Aster laurentianus Fernald is an annual plant endemic to the St. Lawrence e stuary. It typically grows in salt marshes at the periphery of shallow lago ons. In this habitat, the water level fluctuates greatly both within and be tween years. Such fluctuations may induce significant interannual variation s in marsh-plant populations. In this study, we experimentally determined t he effects of different water availability conditions, imposed at various s tages of plant development, on the performance of A. laurentianus. Waterlog ging had no significant effect on net carbon assimilation rate, plant growt h, and biomass allocation. However, a drought stress at the time of reprodu ctive-bud differentiation had a negative effect on flower-head production. We propose that occasional reproductive failures resulting from late-summer droughts may cause significant interannual fluctuations in the size of A. laurentianus populations, potentially making them more susceptible to local extinction.