Plant reproduction in temporary wetlands: the effects of seasonal timing, depth, and duration of flooding

Abstract

In less predictable, drier climates depth, duration and season (month) of flooding influence not only germination and establishment of wetland plants but also completion of the life cycle through to sexual or asexual reproduction. A tank trial was carried out to investigate the effects of season (summer, autumn), duration (0–16 weeks) and depth of flooding (0–60 cm) and their interactions on sexual reproduction of a range of aquatic plant species. Seed bank material was collected from four New England wetlands in New South Wales, Australia. The majority of species germinating and establishing in the summer experiment were able to flower and set seed. In contrast, few of the plants growing during autumn had flowered after 16 weeks and biomass production was significantly reduced. For obligate submerged species flooding duration must be long enough to allow reproductive organs to form and for fertilisation and seed maturation to occur. Amphibious plants, in contrast, in particular those that respond morphologically to water presence or absence, had inflorescences emerging under a wide range of conditions, i.e. out of the water column when submerged, damp or spending only a portion of the life cycle submerged. Terrestrials established in autumn only in the damp treatments. A significant correlation was found for the dominant species from the amphibious and submerged groups between plant biomass and the number of reproductive units produced. Hence, diaspore production of wetland species is often a function of biomass production.