Comparison of the effects of wet N deposition (NH4Cl) and dry N deposition(NH3) on UK moorland species

Increases in N deposition (wet and dry) have been associated with a decline in seminatural plant communities, adapted for growth on nutrient poor soil s in the UK and Europe. The impacts of N deposition applied as either wet N H4+ or gaseous NH3 on vegetation (7 species) from acid moorland in SE Scotl and were compared in a dose-response study. Wet N deposition at 0, 8, 16, 3 2, 64, 128 kg N ha(-1) y(-1) was applied as NH4Cl, and dry deposition as ga seous NH3 (2, 6, 20, 50, 90 mug NH3 m(-3)) under controlled conditions in o pen-top chambers. A strong linear dose-response relationship (p <0.05) was found between foliar N content in all seven plant species and applied NH4-N . However, in the NH3 treatment, only C. vulgaris and P. commune showed a s ignificant response to increasing N additions. NH3 was found to increase th e rate of water loss in Calluna in both autumn and winter by comparison wit h wet deposition. For Eriophorum vaginatum, the NH3 and NH4+ treatments sho wed significant N dose response relationships for biomass. A significant in crease in above ground biomass, proportional to the added N, was found for Narthecium ossifragum when N was applied as NH3 compared to NH4+.