Publikationsdatum:
2011-06-22
Beschreibung:
Although the effects of atmospheric nitrogen deposition on species composition are relatively well known, the roles of the different forms of nitrogen, in particular gaseous ammonia (NH 3 ), have not been tested in the field. Since 2002, we have manipulated the form of N deposition to an ombrotrophic bog, Whim, on deep peat in southern Scotland, with low ambient N (wet + dry = 8 kg N ha −1 y −1 ) and S (4 kg S ha −1 y −1 ) deposition. A gradient of ammonia (NH 3 , dry N), from 70 kg N ha −1 y −1 down to background, 3-4 kg N ha −1 y −1 was generated by free air release. Wet ammonium (NH 4 + , wet N) was provided to replicate plots in a fine rainwater spray (NH 4 Cl at +8, +24, +56 kg N ha −1 y −1 ). Automated treatments are coupled to meteorological conditions, in a globally unique, field experiment. Ammonia concentrations were converted to NH 3 -N deposition (kg N ha −1 ) using a site / vegetation specific parameterization. Within 3 years, exposure to relatively modest deposition of NH 3 , 20-56 kg NH 3 -N ha −1 y −1 led to dramatic reductions in species cover, with almost total loss of Calluna vulgaris , Sphagnum capillifolium and Cladonia portentosa . These effects appear to result from direct foliar uptake and interaction with abiotic and biotic stresses, rather than via effects on the soil. Additional wet N by contrast, significantly increased Calluna cover after 5 years at the 56 kg N dose, but reduced cover of Sphagnum and Cladonia . Cover reductions caused by wet N were significantly different from and much smaller than those caused by equivalent dry N doses. The effects of gaseous NH 3 described here, highlight the potential for ammonia to destroy acid heathland and peat bog ecosystems. Separating the effects of gaseous ammonia and wet ammonium deposition, for a peat bog, have significant implications for regulatory bodies and conservation agencies.
Print ISSN:
1354-1013
Digitale ISSN:
1365-2486
Thema:
Biologie
,
Energietechnik
,
Geographie
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