title: Nitrogen uptake in relation to excess supply and its effects on the lichens Evernia prunastri (L.) Ach and Xanthoria parietina (L.) Th. Fr.
abstract: The aim of this study was to compare the physiological responses to increased nitrogen (N) supply between the nitrophytic lichen Xanthoria parietina (L.) Th. Fr. and the acidophytic lichen Evernia prunastri (L.) Ach. The two lichens were exposed to a weekly dosage of 0.05, 0.1, 0.2, 0.6 or 2.4 g N m(-2) for 2 months, administered as NH(4)NO(3) dissolved in artificial rainwater (1 l m(-2)). After the treatments, in vivo chlorophyll a fluorescence was determined to assess vitality; concentrations of total N, ammonium, nitrate and dominant amino acids, including glutamate, glutamine and arginine, were quantified in order to follow changes in N status; and the polyols ribitol, arabitol and mannitol were quantified to follow changes in the lichens' carbon (C) status. The uptake of N was quantified by labelling the fertiliser with (15)N in the ammonium position; chlorophyll a was used as an indirect marker for algal activity, and ergosterol as an indirect marker of fungal activity. Nitrogen uptake was higher in E. prunastri than in X. parietina, although the latter species may have used the mannitol reserves to obtain C skeletons and energy for N assimilation. Chlorophyll a and ergosterol concentrations remained unaltered in X. parietina irrespective of N dosage while ergosterol decreased with increasing N uptake in E. prunastri. The latter species had accumulated a large pool of ammonium at the highest N dosage, whilst in X. parietina a significant nitrate pool was instead observed. Taken together, these short-term responses to high N supply observed in the two lichens, and the differences between them, can partly explain the higher tolerance of X. parietina towards increased atmospheric N levels.
authors.affiliation: CEBV-Centre for Ecology and Plant Biology, Departamento de Biologia Vegetal, Faculdade de Ciências da Universidade de Lisboa, Bloco C2, Piso 4, 1749-016 Lisboa, Portugal. gaoliveira@fc.ul.pt
authors.forename: Gisela
authors.initials: G
authors.lastname: Gaio-Oliveira
authors.forename: Lena
authors.initials: L
authors.lastname: Dahlman
authors.forename: Kristin
authors.initials: K
authors.lastname: Palmqvist
authors.forename: Maria Amélia
authors.initials: MA
authors.lastname: Martins-Loução
authors.forename: Cristina
authors.initials: C
authors.lastname: Máguas
mesh_terms: D000596:Amino Acids / Q000096:biosynthesis; D002734:Chlorophyll / Q000502:physiology; D000077194:Chlorophyll A; D004875:Ergosterol / Q000378:metabolism; D005308:Fertilizers; D008011:Lichens / Q000378:metabolism / Q000502:physiology*; D008353:Mannitol / Q000378:metabolism; D009566:Nitrates / Q000494:pharmacology; D009584:Nitrogen / Q000378:metabolism / Q000502:physiology*; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D012255:Ribitol / Q000378:metabolism; D013402:Sugar Alcohols / Q000378:metabolism
chemical_list: D000596:Amino Acids; D005308:Fertilizers; D009566:Nitrates; D000644:Quaternary Ammonium Compounds; D013402:Sugar Alcohols; D002734:Chlorophyll; D008353:Mannitol; D012255:Ribitol; D009584:Nitrogen; C006568:ammonium nitrate; D000077194:Chlorophyll A; C014999:arabitol; D004875:Ergosterol