NH3 :: Heather or Ling

Latin name: 
Calluna vulgaris

Impact Type: Direct exposure to pollutant

Key Concerns:

Calluna vulgaris, common throughout the British Isles on acid soils, is present on heaths, moors, bogs and open woods. Elevated concentrations of NH3 may have negative effects on C. vulgaris, as well as on heathland habitats in general. The effects are usually considered as occurring through the contribution of NH3 to N deposition, although direct effects may also occur. Van der Eerden et al. (1991) found that NH3 exposure increased biomass production in Calluna, but that it was at a competitive disadvantage relative to the grass Deschampsia flexuosa which grew faster. Van der Eerden et al. (1991) also raised the concern that NH3 leads to increased frost and drought sensitivity (Peason & Stewart 1993). Such damage to Calluna may result in its decline at the expense of grasses.

However, Calluna can hold its own against grasses except when abiotic stresses (e.g. winter dessication, or attacks by the heather beetle) open up the canopy enabling the grasses to get a foothold under the conditions of improved light. Per unit N, NH3 increases foliar N content more than NH4+ does(Leith et al 2001). In the UK Calluna growing on lowland dry heaths is more at risk form NH3 than Calluna on wet bogs and moors because of the proximity of inland dry heaths (e.g. Thetford and East Anglia) to intensive livestock units. N is likely to increase flower production, shoot growth, and to a lesser extent root growth and litter.

Additional Comments:

Although critical levels for NH3 have been set, Burkhardt et al. (1998) have shown that the critical load for N deposition is usually exceeded first. 

Critical Load/level: 
Habitat/ Ecosystem Type Critical Load/ Level Status Indication of exceedance Reference
Higher plants

3 µg NH3 m-3 annual mean (uncertainty of 2-4 µg NH3 m-3)

UNECE, 2007

Direct visible injury; species composition changes. Ecosystems where sensitive lichens and bryophytes are an important part of the ecosystem integrity, the critical level is set at 1 µg NH3 m-3.

Burkhardt, J.; Sutton, M.A.; Milford, C.; Storeton-West, R.L.; Fowler, D. 1998 Ammonia concentrations at a site in southern Scotland from 2 yr of continuous measurements Atmospheric Environment 32 325-331
Dueck, T.A.; Van der Eerden, L.J.M.; Beemsterboer, B.; Elderson, J. 1991 Nitrogen Uptake and Allocation by Calluna-Vulgaris (L) Hull and Deschampsia-Flexuosa (L) Trin Exposed to 15NH3 Acta Botanica Neerlandica 40 257-267
Leith, I.D.; Sheppard, L.J.; Pitcairn, C.E.R.; Cape, J.N.; Hill, P.W.; Kennedy, V.H.; Tang, Y.S.; Smith, R.I.; D., Fowler 2001 Comparison of the effects of dry deposited N as NH3 with wet deposited N as NH4Cl on acid moorland vegetation. Water Air and Soil Pollution (In press).
Pearson, J.; Stewart, G.R. 1993 The Deposition of Atmospheric Ammonia and Its Effects on Plants New Phytologist 125 283-305
Poser, S.A.; Ashmore, M.R.; Cousins, D.; Sheppard, L.J. 1998 Effects of N additions on the stress sensitivity of Calluna vulgaris. New Phytologist 138 663-673
Sutton, M.A.; Moncrieff, J.B.; Fowler, D. 1992 Deposition of Atmospheric Ammonia to Moorlands. Environmental Pollution 75 15-24
Van der Eerden, L.J.M.; Dueck, T.A.; Berdowski, J.J.M.; Greven, H.; Dobben, H.F. 1991 Influence of HN3 and (HN4)2 SO4 on heathland vegetation Atic Bot Neerl 40 281-296
Species group: 

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