Riders of the storm: Grassland plant response to seawater flooding

Background/Question/Methods - A combination of sea level rise and the increased likelihood of storm surge events associated with anthropogenic climate change is likely to result in more frequent and severe episodes of salt water inundation into low-lying coastal ecosystems. Coastal habitats are both economically and ecologically important, providing protection against the sea for urban areas and agro-ecosystems inland, and offering a refuge for many plant and animal species excluded by intensive agriculture. Consequently the ecological response of coastal ecosystems and species to seawater inundation may have important ramifications not only for conservation, but also coastal management. However, there is remarkably little information on the response of terrestrial coastal plant species to seawater inundation. Our aim was to determine the impact of simulated sea-water inundation on White Clover (Trifolium repens), one of the most common grassland species along European coastlines. In addition, the species is nitrogen fixing (with a potential key role in ecosystem service provision) and an important agronomic species. Using clonal fragments cultivated from parent plants sampled from a natural soil salinity gradient in south Devon, southern England we examined the impact of short-duration seawater flooding (8 or 24 hrs immersion) on short-term (2-day post immersion) changes in leaf salt ion and organic solute concentrations, and longer-term impacts on plant growth (stolon elongation), and flowering (up to 70 days post-immersion).

Results/Conclusions

There was substantial Cl^- and Na⁺ accumulation in clover leaves, especially for plants subjected to 24 h immersion, but no consistent variation linked to parent plant provenance along the salinity gradient. Proline and sucrose concentrations also increased in plants following clover immersion which indicates a potential for solute accumulation as a response to the osmotic imbalance caused by salt ion accumulation. Both Trifolium growth and flowering (mean number of inflorescences per plant) were reduced by longer immersion times, but plants originating from more saline soils responded less negatively than those from lower salinity soils. The accumulation of proline and sucrose coupled with variation in clover growth and flowering responses points to an adaptive capacity for tolerance of seawater flooding in T. repens. More generally however, any species-specific variation in response to sea water flooding would likely have profound implications for coastal ecosystems. The loss of particularly susceptible species would not only reduce biodiversity but impact upon ecosystem stability and so resilience of the vegetation to further perturbations.