Atmospheric nitrogen deposition promotes carbon loss from peat bogs

doi:10.1073/pnas.0606629104

Atmospheric nitrogen deposition promotes carbon loss from peat bogs

^aDepartment of Biology and Evolution, University of Ferrara, Corso Ercole I d'Este 32, I-44100 Ferrara, Italy;
^cSchool of Biological Sciences, University of Wales, Bangor LL57 2UW, United Kingdom;
^dDepartment of Plant Ecology, Evolutionary Biology Centre, Uppsala University, Villavägen 14, SE752 36 Uppsala, Sweden;
^eNature Conservation and Plant Ecology Group, Wageningen University, Bornsesteeg 69, NL-6708 PD Wageningen, The Netherlands;
^fInstitute of Botany and Zoology, Faculty of Science, Masaryk University, Kotlářská 2, CZ-61137 Brno, Czech Republic;
^gDepartment of Ecology, Institute of Botany, Academy of Sciences of the Czech Republic, Poříčí 3B, CZ-60300 Brno, Czech Republic;
^hInstitute of Botany, Academy of Sciences of the Czech Republic, Dukelská 135, CZ-37982 Třeboň, Czech Republic;
ⁱFaculty of Biological Sciences, University of South Bohemia, Branišovská 31, CZ-37005 České Budějovice, Czech Republic;
^jDepartment of Earth Sciences, University of Parma, Parco Area delle Scienze 157, I-43100 Parma, Italy;
^kDepartment of Forest Ecology, Slovenian Forestry Institute, Večna pot 2, SI-1000 Ljubljana, Slovenia; and
^lDepartment of Biology, University of Joensuu, PO Box 111, FIN-80101 Joensuu, Finland

Edited by F. Stuart Chapin III, University of Alaska, Fairbanks, AK, and approved October 30, 2006 (received for review August 2, 2006)

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 ≈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.

Footnotes

^bTo whom correspondence should be addressed. E-mail: luca.bragazza{at}unife.it
Author contributions: L.B. and C.F. designed research; L.B., T.J., H.R., J.L., N.F., T.E., M.H., T.H., P.I., L.K., T.T., and H.T. performed research; L.B., C.F., T.J., H.R., J.L., N.F., T.E., R.G., M.H., T.H., P.I., L.K., T.T., and H.T. analyzed data; and L.B. and C.F. wrote the paper.
The authors declare no conflict of interest.
Abbreviations:

DOC,

dissolved organic carbon;

MUF,

methylumbelliferyl.