Unraveling plant strategies in tidal marshes by investigating plant traits and environmental conditions

Abstract

Aims: Tidal marsh vegetation along estuaries is exposed to strong environmental gradients that determine which species — enabled through specific traits — can establish and persist. With these ecosystems under anthropogenic pressure, in-depth knowledge on the conservation of remaining tidal wetlands and restoration potentials is needed. In this study we elaborate the habitat conditions in the natural vegetation of the Elbe estuary and analyze: (a) which abiotic factors drive species composition; and (b) which species traits are key to the plants’ strategies in this specific ecotone. Location: Three sites in the Elbe estuary (river kilometer 671–703). Methods: We collected data on soil nutrients, inundation period and wave height and sampled traits of the 17 most abundant plant species, which we analyzed by RLQ (three-table analysis, including environment variables [R], species abundance [L] and a species traits table [Q]). Results: We detected a strong ˈwave–disturbance–inundation gradientˈ, which separated sparsely vegetated low-lying plots receiving high wave impact and exposed to long inundation periods, from high-lying plots showing dense vegetation and aerated soils. Close to the shore, plants showed low organ density and high investment into rhizomes, with a correlation of 0.72 between mass fraction of rhizome and phosphorus content of rhizome tissue. On higher elevations, plants strongly expressed traits relating to competition, like high allocation to stem biomass. Further, we found species with high leaf chlorophyll content showing low specific leaf area values and a negative correlation with the nutrient gradient. Conclusion: The results of our study are particularly relevant for restoration measures in order to re-establish healthy marsh vegetation. However, changes in the environmental conditions, for instance stronger wave energies by a higher shipping frequency in the river channel and sea level rise may trigger changes in species composition through plant trait adaptations, for example by demanding a stem flexibility beyond what would be structurally feasible.