title: Atmospheric nitrogen deposition promotes carbon loss from peat bogs.
abstract: Peat bogs have historically represented exceptional carbon (C) sinks because of their extremely low decomposition rates and consequent accumulation of plant remnants as peat. Among the factors favoring that peat accumulation, a major role is played by the chemical quality of plant litter itself, which is poor in nutrients and characterized by polyphenols with a strong inhibitory effect on microbial breakdown. Because bogs receive their nutrient supply solely from atmospheric deposition, the global increase of atmospheric nitrogen (N) inputs as a consequence of human activities could potentially alter the litter chemistry with important, but still unknown, effects on their C balance. Here we present data showing the decomposition rates of recently formed litter peat samples collected in nine European countries under a natural gradient of atmospheric N deposition from approximately 0.2 to 2 g.m(-2).yr(-1). We found that enhanced decomposition rates for material accumulated under higher atmospheric N supplies resulted in higher carbon dioxide (CO2) emissions and dissolved organic carbon release. The increased N availability favored microbial decomposition (i) by removing N constraints on microbial metabolism and (ii) through a chemical amelioration of litter peat quality with a positive feedback on microbial enzymatic activity. Although some uncertainty remains about whether decay-resistant Sphagnum will continue to dominate litter peat, our data indicate that, even without such changes, increased N deposition poses a serious risk to our valuable peatland C sinks.
authors.affiliation: Department of Biology and Evolution, University of Ferrara, Corso Ercole I d'Este 32, I-44100 Ferrara, Italy. luca.bragazza@unife.it
authors.forename: Luca
authors.initials: L
authors.lastname: Bragazza
authors.forename: Chris
authors.initials: C
authors.lastname: Freeman
authors.forename: Timothy
authors.initials: T
authors.lastname: Jones
authors.forename: Håkan
authors.initials: H
authors.lastname: Rydin
authors.forename: Juul
authors.initials: J
authors.lastname: Limpens
authors.forename: Nathalie
authors.initials: N
authors.lastname: Fenner
authors.forename: Tim
authors.initials: T
authors.lastname: Ellis
authors.forename: Renato
authors.initials: R
authors.lastname: Gerdol
authors.forename: Michal
authors.initials: M
authors.lastname: Hájek
authors.forename: Tomás
authors.initials: T
authors.lastname: Hájek
authors.forename: Paola
authors.initials: P
authors.lastname: Iacumin
authors.forename: Lado
authors.initials: L
authors.lastname: Kutnar
authors.forename: Teemu
authors.initials: T
authors.lastname: Tahvanainen
authors.forename: Hannah
authors.initials: H
authors.lastname: Toberman
mesh_terms: D001272:Atmosphere / Q000737:chemistry*; D002245:Carbon Dioxide / Q000032:analysis*; D005060:Europe; D017752:Greenhouse Effect; D008954:Models, Biological; D009584:Nitrogen / Q000032:analysis*; D010758:Phosphorus / Q000032:analysis; D012987:Soil / Q000032:analysis*; D013057:Spectrum Analysis; D053833:Wetlands
chemical_list: D012987:Soil; D002245:Carbon Dioxide; D010758:Phosphorus; D009584:Nitrogen