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Research article2010Peer reviewed

Responses of epiphytic lichens to an experimental whole-tree nitrogen-deposition gradient

Johansson, Otilia; Nordin, Annika; Olofsson, Johan; Palmqvist, Kristin

Abstract

P>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.

Keywords

15N-labeled ammonium nitrate; Alectoria sarmentosa; Chla; critical load; lichen sensitivity; phosphorus; Platismatia glauca; simulated nitrogen deposition

Published in

New Phytologist
2010, Volume: 188, number: 4, pages: 1075-1084
Publisher: WILEY-BLACKWELL PUBLISHING, INC