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

TitleOrganic matter transformation in the peat column at Marcell Experimental Forest: Humification and vertical stratification
Publication TypeJournal Article
Year of Publication2014
AuthorsTfaily, MM, Cooper, WT, Kostka, JE, Chanton, PR, Schadt, CW, Hanson, PJ, Iversen, CM, Chanton, JP
JournalJOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES
Volume119
Pagination661-675
Date PublishedAPR 28
Type of ArticleArticle
ISSN2169-8953
KeywordsFT-IR spectroscopy, humification, NMR spectroscopy, organic matter, peatlands, vertical stratification
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 C-13 nuclear magnetic resonance (NMR) spectroscopy) and related these changes to decomposition proxies C:N ratio, C-13 and N-15, 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, C-13 and N-15, 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 22 degrees C 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.

DOI10.1002/2013JG002492