|Title||Organic matter transformation in the peat column at Marcell Experimental Forest: Humification and vertical stratification|
|Publication Type||Journal Article|
|Year of Publication||2014|
|Authors||Tfaily MM, Cooper WT, Kostka JE, Chanton PR, Schadt CW, Hanson PJ, Iversen CM, Chanton JP|
|Journal||Journal of Geophysical Research: Biogeosciences|
|Keywords||FT-IR spectroscopy, humification, NMR spectroscopy, organic matter, peatlands, vertical stratification, Wetlands|
We characterized peat decomposition at the Marcell Experimental Forest (MEF), Minnesota, USA, to a depth of 2 m 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 δ15N, bulk density, and water content. FT IR determined that peat humification increased rapidly between 30 and 75 cm, 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 75 cm, 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°C revealed the highest methane production rates, greatest CH4:CO2production ratios, and significant O‐alkyl‐C utilization within this 30 and 75 cm 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.