Seawater spray as a significant nitrogen source across coastal dune vegetation gradients

Background

Nitrogen significantly influences plant performance and vegetation development in nutrient-poor ecosystems like coastal dunes. While various sources contribute nitrogen, including N₂ fixation and marine inputs, the significance of seawater spray remains understudied. In this study, we aimed to assess the relevance of seawater spray as a source of nitrogen input and its potential role in plant community composition in dune ecosystems.

Methods

The δ¹⁵N, δ¹³C, N, and C content of leaves from the most abundant 21 species were measured in 6 positions across a beach inland gradient in a Mediterranean dune system in SW Spain. Soil samples at different depths were collected in each position and N, C, P, K, NH4⁺, NO3⁼, and organic matter were measured. Salt spray accumulation was determined on Achillea maritima leaves across the gradient.

Results

Leaf nitrogen content did not exhibit a beach-inland gradient, but δ¹⁵N decreased with distance from the sea. Species displayed three distinct N uptake strategies along the gradient: species from Upper Beach and Foredune communities showed high δ¹⁵N values, suggesting a marine origin; species distributed across the gradient exhibited decreasing δ¹⁵N patterns from the Upper Beach to the Inland, indicative of seawater spray influence; species farthest from the sea relied on non-marine nitrogen sources.

Conclusions

These results indicate the importance of seawater nitrogen income for the dune system vegetation and evidence that dune plant species exhibit varied N uptake strategies influenced by their position across the beach-inland gradient.