Climatic modifiers of the response to nitrogen deposition in peat-forming Sphagnum mosses: a meta-analysis
Limpens, J. | Granath, G. | Gunnarsson, U. | Aerts, R. | Bayley, S. | Bragazza, L. | Bubier, J. | Buttler, A. | van den Berg, L.J.L. | Francez, A.J. | Gerdol, R. | Grosvernier, P. | Heijmans, M.M.P.D. | Hoosbeek, M.R. | Hotes, S. | Ilomets, M. | Leith, I. | Mitchell, E.A.D. | Moore, T. | Nilsson, M.B. | Nordbakken, J.F. | Rochefort, Line | Rydin, H. | Sheppard, L.J. | Thormann, M. | Wiedermann, M.M. | Williams, B.L. | Xu, B.
• Peatlands in the northern hemisphere have accumulated more atmospheric carbon (C) during the Holocene than any other terrestrial ecosystem, making peatlands long-term C sinks of global importance. Projected increases in nitrogen (N) deposition and temperature make future accumulation rates uncertain. • Here, we assessed the impact of N deposition on peatland C sequestration potential by investigating the effects of experimental N addition on Sphagnum moss. We employed meta-regressions to the results of 107 field experiments, accounting for sampling dependence in the data. • We found that high N loading (comprising N application rate, experiment duration, background N deposition) depressed Sphagnum production relative to untreated controls. The interactive effects of presence of competitive vascular plants and high tissue N concentrations indicated intensified biotic interactions and altered nutrient stochiometry as mechanisms underlying the detrimental N effects. Importantly, a higher summer temperature (mean for July) and increasedannual precipitation intensified the negative effects of N. The temperature effect was comparable to an experimental application of almost 4 g N m⁻² yr⁻¹ for each 1°C increase. • Our results indicate that current rates of N deposition in a warmer environment will strongly inhibit C sequestration by Sphagnum-dominated vegetation.
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