Soil as a potential source of nitrogen for mat-forming lichens

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Abstract
A field experiment is described, the aim of which was to assess the extent of nitrogen (N) movement from heathland soil upwards into terricolous mat-forming lichens. A molten agar solution of either 15N-labelled glycine or 15N-labelled ammonium (as NH4Cl) was injected onto the soil surface beneath undisturbed cushions of Cladonia por tentosa (Dufour) Coem. Lichen thalli were recovered after 9 months and analysed for 15N content. There was no evidence of 15N uptake by the lichen, though 15N was taken up by vascular plants rooted beneath the lichen cushions. The results suggest that C. portentosa does not compete effectively for soil N. This refutes the conclusions of previous studies, which inferred the efficient uptake of soil organic N by mat-forming lichens based on values of δ15N.Key words: ammonium, lichens, 15N, organic nitrogen, soil nutrients.