Heathland vegetation as a bio-monitor for nitrogen deposition and source attribution using δ15N values

The %N and δ15N signals in foliar nitrogen (N) from four heathland species have been monitored in a blanket bog plant community subjected to different experimental inputs of wet and dry N deposition. Interactions with combined additional treatments of phosphorus (P) and potassium (K) were also investigated. Calluna vulgaris, Cladonia portentosa, Sphagnum capillifolium and Hypnum cupressiforme were harvested for 15N analysis prior to wet and dry treatment applications and again after 16 months field exposure. A significant increase was observed in both %N and δ15N values for all plant species in response to both wet and dry treatments whilst PK additions also produced significant decreases in foliar %N and associated δ15N values for several of the species sampled. These enrichments in the δ15N signals for post-treatment shoot tissue were attributable to the δ15N signal in the source application, a finding of potential value in using bio-monitors for assessment of N deposition.