Is lichen δ15N an indicator of nitrogen pollution and a surrogate of nitrogen atmospheric composition? Evidence from manipulative experiments

Silvana Munzi1, Cristina Branquinho1, Cristina Cruz1, Cristina Máguas1, Ian Leith2, Lucy Sheppard2, Mark Sutton2

1 Centre for Ecology, Evolution and Environmental Changes (cE3c), Faculdade de Ciências, Universidade de Lisboa, Bloco C2, 5º Piso, sala 2.5.14, 1749-016 Lisbon, Portugal

2 Centre for Ecology & Hydrology (CEH) Edinburgh, Bush Estate, Penicuik, EH26 0QB, UK


Due to the relevance of nitrogen (N) as a pollutant, setting up an effective method to determine spatial distribution of N sources would help to develop management and mitigation strategies. Although promising, the use of isotopic signature of lichens to map atmospheric N deposition is still difficult due to the synergism between climatic and anthropogenic factors and the superimposition of multiple N sources. To understand how lichen’s isotopic signature is affected by N, thalli of the sensitive Evernia prunastri and of the tolerant Xanthoria parietina were exposed for ten weeks to different forms and doses of N in a manipulative experiment, and physiological parameters, total N, δ15N and chlorophyll a fluorescence were measured. In parallel, thalli of Cladonia portentosa exposed to the same treatments for 11 years or 6 months were analyzed to investigate the role of time of exposure. Our results showed that lichen N content and δ15N were correlated with the N dose of the N treatments and that lichen δ15N tended to become similar to the source’s signature. However, nitrophytic and acidophytic species showed different δ15N in response to the same treatments, probably due to their cation exchange capacity. Finally, the correlation between N content and δ15N was higher in case of long-term exposure. Nitrogen isotopic signature in lichens can potentially be used as indicator to determine spatial distribution of N sources in the field. However, further investigation is needed to confirm these results in the field, and species functional traits must be taken in particular consideration.