Description:
Many plant species benefit from symbioses with mycorrhizal fungi, which enhance nutrient exploration and uptake and protect roots from pathogens and drought. In ectomycorrhizal (ECM) plants the fungal hyphae enclose the plant root as a fungal mantle and penetrate between the epidermal and cortical cells of the root axis to form the 'Hartig net'. The ECM fungi that produce large above-ground fruitbodies are usually associated with trees. N deposition can affect fruit body formation, the production and distribution of the extra radical mycelium in the soil and the formation of ECM (Wallenda & Kottke 1998).
Data from long-term N deposition studies have shown loss of species diversity both above and below-ground. 'Generalist' species, forming a symbiosis with a wide range of tree species are less affected than 'specialist' species. The negative effects on ECM reflect high concentrations of N in the soil.
Previous experience:
Observations of the effects of an N manipulation experiment at CEH Edinburgh have shown varying effects depending on whether the N supplied as NH4NO3 is also supplied with sulphuric acid. In addition the responses have changed as the stand has aged so that the initial restriction of the ECM species Lactarius rufus and domination by Tylospora fibrillose has become less obvious as the stand has aged (Ingleby pers comm.).
Ritter (1990) observed that ECM fruit bodies associated with Pinus sylvestris ceased to occur within a certain distance of a pig farm, i.e. they only occurred at lower levels of N deposition. Lilleskov & Fahey (1996) measured an N gradient around a fertilizer factory in Alaska and found that Laccaria laccata, L bicolour, Lactarius theiogalus and Paxillus involutris were to be found all along this gradient whereas Cortinairus spp and Russulas declined drastically in both abundance and diversity with increasing N deposition.
Suitability to indicate atmospheric concentrations:
Insufficient evidence.
Suitability to indicate atmospheric depositions:
Some evidence with scope for development.
Suitability to indicate environmental impacts:
Some evidence with scope for development. By definition the method assesses a biological response to nitrogen.
Sensitivity to other factors:
The presence of ECM fungi is affected by temperature and moisture levels and site history.
Timescale:
The method probably reflects a long term response (several years to decades).
Limitations:
The presence of ECM fungi species depends on the presence of a suitable host plant species. Because of seasonal and annual variations in fruiting, sites must be visited regularly to check for ECM fruiting bodies.
Expertise in field:
The method requires skilled personnel to correctly identify fungal fruiting bodies. However training could be provided in fungal identification.
Expertise in laboratory:
Further fungal identification may be necessary in the laboratory requiring specialist skills.
Cost (per unit sample): £unknown
Cost Comment: Insufficient information available.
Robustness: 
