Seedling stability in waterlogged sediments: an experiment with saltmarsh plants

Abstract

Saltmarsh seedlings are exposed to extreme soil conditions in combination with mechanical disturbance by waves and tides, especially at the seaward fringe. We tested whether soil waterlogging affects resistance of seedlings against physical disturbance, thereby potentially influencing the distribution of saltmarsh species. A greenhouse experiment was conducted to investigate effects of waterlogging on plant traits, in particular root growth, and tolerance of seedlings against sediment erosion. Three species, each dominating different elevations in NW European salt marshes (Salicornia europaea, Atriplex portulacoides and Elytrigia atherica), were selected for the experiments. Individual seedlings were grown under different waterlogging treatments and finally subjected to an erosion treatment. The depth of erosion at which the seedlings toppled (Ecrit) was determined and related to above-and below-ground morphological traits of the seedlings. Resistance against erosion decreased in all three species from drained to completely waterlogged soil conditions, with the strongest negative impact of waterlogging on the upper marsh species E. atherica. Root length and biomass, shoot biomass and the root:shoot biomass ratio were the most important traits positively affecting Ecrit. The experiment demonstrates that rapid root growth is essential for the stability of seedlings, which is presumably of great importance for their successful establishment on tidal flats where sediment erosion may be a limiting factor. Root growth, in turn, is affected by a species-specific response to waterlogging. Our study suggests that this species-specific effect of waterlogging on seedling stability contributes to species sorting along the inundation gradient of coastal ecosystems.

Salt marsh establishment in poorly consolidated muddy systems: effects of surface drainage, elevation, and plant age

“…Both observations were in accordance with theoretical expectations that such fine muddy soil cannot lose much interstitial water during a single ebb tide (see references in introduction). This makes present study starkly contrast to earlier works on drainage effects on salt marshes in systems with relatively coarse sediments (for salt marshes in peaty soils see Mendelssohn and Seneca 1980; for salt marshes in sandy soil, see Padgett et al 1998, Padgett and Brown 1999, Redelstein et al 2018) that have a high hydraulic conductivity and therefore can reduce water saturation as a consequence of vertical draining of sediment. The grain size (with a D 50 of 27.62 μm, silt content T 63 of 62.68%) of the sediment in our system was too fine, and the hydraulic conductivity consequently too low, to allow for substantial drainage of interstitial water from the sediment during the low water period (Winterwerp andKesteren 2004, Ren andSantamarina 2018).…”

“…2003al. , Fivash et al 2020) and thereby relieve sulfide toxicity to seedling roots (Redelstein et al 2018) that lack aerenchyma (Burdick andMendelssohn 1987, Jung et al 2008). Drainage effects are generally observed in coarse sand or peaty sediments (see, e.g., Mendelssohn and Seneca [1980] for peat soil; and Padgett et al [1998], Padgett and Brown [1999] in artificial sandy sediments), where hydraulic resistance of the sediment is typically low and capillary forces in the wide pores are restricted, causing interstitial water to drain vertically from the sediment (Winterwerp and Kesteren 2004).…”

Spatial and temporal patterns of initial plant establishment in salt marsh communities

“…After seed arrival, the seedling’s emergence and survival are related to environmental factors such as inundation regime (Pétillon et al ., 2010), hydrodynamic conditions (Mateos‐Naranjo et al ., 2008; Redelstein et al ., 2018), sediment stability (Bouma et al ., 2013; Cao et al ., 2018) and salinity (Shumway & Bertness, 1992; Dethier & Hacker, 2005; Hughes et al ., 2012). Lower water storage of the sandy tidal‐flat sediments could be causing unsuitable soil moisture and salinity conditions during periods of germination, especially in the upper elevations with higher groundwater levels and infrequent inundation.…”

El Niño Increases High‐Tide Flooding in Tidal Wetlands Along the U.S. Pacific Coast

“…Marsh annuals, including exotic species, could especially benefit from this salinity reduction (Kuhn & Zedler, ). Greater inundation could also affect seedling morphology and survivorship (Redelstein et al, ) or the direction or intensity of interactions between species after the germination period (Keammerer & Hacker, ). Because changes in inundation could impact other abiotic gradients of importance to plant productivity and composition and have differing effects on different life stages, further research is needed on how flooding variability impacts establishment, productivity, and interspecific interactions across a variety of plant species.…”