Dry deposition of ammonia gas drives species change faster than wet deposition of ammonium ions: evidence from a long-term field manipulation

摘要: Although the effects of atmospheric nitrogen deposition on species composition are relatively well known, roles of different forms nitrogen, in particular gaseous ammonia (NH3), have not been tested field. Since 2002, we manipulated form N to an ombrotrophic bog, Whim, deep peat southern Scotland, with low ambient (wet + dry = 8 kg ha 1 yr 1) and S (4 deposition. A gradient ammonia (NH3, N), from 70 yr 1 down background, 3–4 was generated by free air release. Wet ammonium (NH4 +, wet N) provided replicate plots a fine rainwater spray (NH4Cl at +8, +24, +56 yr 1). Automated treatments coupled meteorological conditions, globally unique, field experiment. Ammonia concentrations were converted NH3-N (kg ha 1) using site/vegetation specific parameterization. Within 3 years, exposure modest NH3, 20–56 yr 1 led dramatic reductions cover, with almost total loss Calluna vulgaris, Sphagnum capillifolium Cladonia portentosa. These appear result direct foliar uptake interaction abiotic biotic stresses, rather than via soil. Additional contrast, significantly increased cover after 5 years at the 56 dose, but reduced Cladonia. Cover caused significantly different much smaller those equivalent doses. The NH3 described here, highlight potential for destroy acid heathland bog ecosystems. Separating effects of deposition, has significant implications regulatory bodies and conservation agencies