Nitrogen Deposition

Soil gas fluxes


The gases NO and N2O are produced in soils by nitrifying and denitrifying bacteria, and the magnitude of the emissions is controlled by the availability of N as ammonium (NH4) or nitrate (NO3) and also by certain climatic and soil properties which promote nitrification or denitrification, e.g. temperature, rainfall, organic matter content (Skiba & Smith 2000).

N:P ratio in leaf tissues


Where plant growth may be limited by P availability or when enhanced N deposition may lead to reduced availability and/or uptake, measurements of the N:P ratios in selected species may provide a better indication of N saturation. Optimum N:P ratios for plant growth range from 10-14 (van den Driesshe, 1974; Ingestad, 1979). Low ratios (<10) indicate N limited growth and high ratios (>14) indicate P limitation (Koerselma & Meuleman, 1996).

Previous experience:

Lichen Diversity (Verein Deutscher Ingenieure (VDI) method)


The VDI approach is a standardized German method that was devised to assess changes in lichen communities over wide geographical areas in order to assess the influence of air pollution in Central Europe. The method is based on the frequency of occurrence of selected widespread lichen species within a unit area on selected tree trunks.

Lichen Diversity (Deviation from Naturality)


A method developed in Italy to assess deviation from natural lichen diversity on trees in sites within a homogeneous bioclimatic area. LD is calculated using the sum of frequencies on trees of the same species within 10 samples of units 15 cm x 10 cm (30 cm x 50 cm) and the mean calculated from the number of relevees. A 5-scale class of deviation from naturality is based on % deviation from the natural LD values in the area and can be correlated with climatic, land management and pollution data. Loppi et al. (2003)

Lichen Diversity (Ellenberg Method)


Additional nitrogen supply both leads to a eutrophication of tree bark and changes in bark pH. In particular, enhanced levels of NH3 have been shown to increase bark pH. The environmental preferences of lichens in relation to these different conditions may be classified into two extremes: 'nitrophyte' lichen species prefer high supply of nitrogen and high bark pH, while 'acidophyte' lichen species prefer a low supply of nitrogen and the naturally low pH of clean bark.

Lichen Diversity (Lichens on twigs method)


Twigs provide a new substrate every year and colonising lichen communities are strongly affected by existing climatic and atmospheric conditions as well as by availability of propagules. Data on lichen diversity from a standard sampling procedure along woodland and or hedgerow margins allows a comparison of lichen communities in the vicinity of a range of environmental conditions, particularly those associated with agricultural conditions. The procedure is repeatable allowing an assessment of changes over time.


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