Increases in N deposition (wet and dry) have been associated with a decline in semi-natural plant communities, adapted for growth on nutrient poor soils in the UK and Europe. The impacts of N deposition applied as either wet NH_4^+ or gaseous NH_3 on vegetation (7 species) from acid moorland in SE Scotland were compared in a dose-response study. Wet N deposition at 0, 8, 16, 32, 64, 128 kg N ha^−1 y^−1 was applied as NH_4Cl, and dry deposition as gaseous NH_3 (2, 6, 20, 50, 90 µg NH_3 m^−3) under controlled conditions in open-top chambers. A strong linear dose-response relationship (p<0.05) was found between foliar N content in all seven plant species and applied NH_4-N. However, in the NH_3 treatment, only C. vulgaris and P. commune showed a significant response to increasing N additions. NH_3 was found to increase the rate of water loss in Calluna in both autumn and winter by comparison with wet deposition. For Eriophorum vaginatum, the NH_3 and NH_4^+ treatments showed significant N dose response relationships for biomass. A significant increase in above ground biomass, proportional to the added N, was found for Narthecium ossifragum when N was applied as NH_3 compared to NH_4^+.\ud \u
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