MEPS 590:95-108 (2018)  -  DOI: https://doi.org/10.3354/meps12463

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 to physical disturbance, thereby potentially influencing the distribution of saltmarsh species. A mesocosm experiment was conducted to investigate effects of waterlogging on plant traits, in particular root growth, and tolerance of seedlings to 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 (E_crit) was determined and related to above- and below-ground morphological traits of the seedlings. Resistance to erosion decreased in all 3 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 E_crit. The experiment demonstrates that rapid root growth is essential for the stability of seedlings, and is presumably of great importance for their successful establishment on tidal flats where sediment erosion may be a limiting factor. Root growth  is in turn 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.

KEY WORDS: Coastal ecosystems · Erosion · Root growth · Species distribution · Tidal inundation · Vegetation establishment