The purpose of this experiment was to investigate the survival and biomass accumulation of wetland plant species under different water depths in controlled microcosms. In the greenhouse, two-week-old seedlings were randomly assigned to one of seven water-depth treatments (-6, -4, -2, 0, +2, +4, and +6 cm relative to the soil surface) and allowed to grow for six months. Species included five perennial sedges, four perennial and one annual grasses, and two perennial and two annual forbs. Twelve of the species had their lowest biomass and lowest survivorship at water depths greater than 0 cm. The root:shoot ratio, however, did not change across water-depth treatments. Biomass accumulation differed by plant form (sedges > forbs > grasses). Annuals had the greatest biomass values across the widest range of water depths compared to perennials. Of the fourteen plants tested, Lythrum salicaria (purple loosestrife), one of the two invasive, non-native species tested, had the greatest biomass at water depths from -6 to +2, whereas Phalaris arundinacea (reed canarygrass), the other invasive, had comparatively small mean biomass values. Ranking of biomass between species was highly concordant between non-flooded treatments but not significantly concordant between flooded treatments indicating that plant species have distinct responses to flooding. This research suggests that newly established plant seedlings in wetland restorations should not be submerged, or if submergence is unavoidable, annuals and sedges may be more tolerant of prolonged flooding.
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