Organic matter transformation in the peat column at Marcell Experimental Forest: Humification and vertical stratification

Malak M. Tfaily, William T. Cooper, Joel E. Kostka, Patrick R. Chanton, Christopher W. Schadt, Paul J. Hanson, Colleen M. Iversen, Jeffrey P. Chanton

Research output: Contribution to journalArticlepeer-review

112 Scopus citations

Abstract

We characterized peat decomposition at the Marcell Experimental Forest (MEF), Minnesota, USA, to a depth of 2m to ascertain the underlying chemical changes using Fourier transform infrared (FT IR) and 13C nuclear magnetic resonance (NMR) spectroscopy) and related these changes to decomposition proxies C:N ratio, δ13C and δ 15N, bulk density, and water content. FT IR determined that peat humification increased rapidly between 30 and 75cm, indicating a highly reactive intermediate-depth zone consistent with changes in C:N ratio, δ13C and δ15N, bulk density, and water content. Peat decomposition at the MEF, especially in the intermediate-depth zone, is mainly characterized by preferential utilization of O-alkyl-C, carboxyl-C, and other oxygenated functionalities with a concomitant increase in the abundance of alkyl- and nitrogen-containing compounds. Below 75cm, less change was observed but aromatic functionalities and lignin accumulated with depth. Significant correlations with humification indices, identified by FT IR spectroscopy, were found for C:N ratios. Incubation studies at 22C revealed the highest methane production rates, greatest CH4:CO2 production ratios, and significant O-alkyl-C utilization within this 30 and 75cm zone. Oxygen-containing functionalities, especially O-alkyl-C, appear to serve as excellent proxies for soil decomposition rate and should be a sensitive indicator of the response of the solid phase peat to increased temperatures caused by climate change and the field study manipulations that are planned to occur at this site. Radiocarbon signatures of microbial respiration products in deeper pore waters at the MEF resembled the signatures of more modern dissolved organic carbon rather than solid phase peat, indicating that recently photosynthesized organic matter fueled the bulk of subsurface microbial respiration. These results indicate that carbon cycling at depth at the MEF is not isolated from surface processes. Key Points Physical, chemical, and spectroscopic properties of bog peat were characterized

Original languageEnglish (US)
Pages (from-to)661-675
Number of pages15
JournalJournal of Geophysical Research: Biogeosciences
Volume119
Issue number4
DOIs
StatePublished - Apr 2014
Externally publishedYes

Keywords

  • FT-IR spectroscopy
  • humification
  • NMR spectroscopy
  • organic matter
  • peatlands
  • vertical stratification

ASJC Scopus subject areas

  • Soil Science
  • Forestry
  • Water Science and Technology
  • Palaeontology
  • Atmospheric Science
  • Aquatic Science
  • Ecology

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