title: Responses of epiphytic lichens to an experimental whole-tree nitrogen-deposition gradient.
abstract: Here, we examined the responses of the epiphytic lichens Alectoria sarmentosa and Platismatia glauca to increased atmospheric nitrogen (N) deposition in an old-growth boreal spruce forest, to assess the sensitivity of these species to N and define their critical N load. Nitrogen deposition was simulated by irrigating 15 trees over a 3 yr period with water and isotopically labeled NH(4)NO(3), providing N loads ranging from ambient to 50 kg N ha(-1) yr(-1) . Thallus N concentration increased in both species with increasing N load, and uptake rates of both NH(4)(+) and NO(3)(-) were similar. Photobiont concentration increased linearly with increased N in both species, saturating in A. sarmentosa in the third year at the highest N loads (25 and 50 kg ha(-1) yr(-1)). The simulated N deposition decreased the phosphorus (P) concentration in A. sarmentosa, and increased the N:P ratio in both species. Significant responses in lichen chemistry were detected to inputs of 12.5 kg N ha(-1) yr(-1) or higher, suggesting that resources other than N limit lichens at higher N loads. However, the data also suggest that N saturation may be cumulative over time, even at low N.
authors: Department of Ecology and Environmental Science (EMG), Umeå University, SE-901 87 Umeå, Sweden. otilia.johansson@emg.umu.se
authors: Otilia
authors: O
authors: Johansson
authors: Annika
authors: A
authors: Nordin
authors: Johan
authors: J
authors: Olofsson
authors: Kristin
authors: K
authors: Palmqvist
mesh_terms: D000704:Analysis of Variance; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D005843:Geography; D008011:Lichens / Q000502:physiology*; D009584:Nitrogen / Q000378:metabolism*; D010758:Phosphorus / Q000378:metabolism; D018515:Plant Leaves / Q000378:metabolism; D011891:Rain; D012621:Seasons; D013548:Sweden; D013696:Temperature; D014197:Trees / Q000378:metabolism*; D014867:Water
chemical_list: D014867:Water; D002734:Chlorophyll; D010758:Phosphorus; D009584:Nitrogen; D000077194:Chlorophyll A