Reduction‐Oxidation Potential and Dissolved Organic Matter Composition in Northern Peat Soil: Interactive Controls of Water Table Position and Plant Functional Groups

• Published in: Journal of geophysical research. Biogeosciences Vol. 124; no. 11; pp. 3600 - 3617
• Main Authors: Kane, E. S., Veverica, T. J., Tfaily, M. M., Lilleskov, E. A., Meingast, K. M., Kolka, R. K., Daniels, A. L., Chimner, R. A.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-11-2019
• Subjects: Atmosphere; Carbon; Carbon cycle; Carbon dioxide; Chemical synthesis; Climate; Climate change; Climate system; Composition effects; Cyperaceae; dissolved organic carbon; Dissolved organic matter; Earth; Ecosystems; Electrode potentials; Functional groups; Greenhouse effect; Greenhouse gases; Groundwater table; Interactive control; Mesocosms; Metabolism; Molecular weight; Nitrogen; Organic matter; Organic soils; Oxidation; Oxidoreductions; Peat; Peat soils; Peatlands; phenolic; Phenolic compounds; Phenols; Plant communities; Plant species; Redox potential; Reduction; Shrubs; Soil; Soil water; Soils; Species composition; Sugar; tyrosine; Water level fluctuations; Water levels; Water table
• DOI: 10.1029/2019JG005339
• EISSN: 2169-8961
• ISSN: 2169-8953

Globally important carbon (C) stores in northern peatlands are vulnerable to oxidation in a changing climate. A growing body of literature draws attention to the importance of dissolved organic matter (DOM) in governing anaerobic metabolism in organic soil, but exactly how the reduction‐oxidation (redox) activities of DOM, and particularly the phenolic fraction, are likely to change in an altered climate remain unclear. We used large mesocosms in the PEATcosm experiment to assess changes in peatland DOM and redox potential in response to experimental manipulations of water table (WT) position and plant functional groups (PFGs). WT position and PFGs interacted in their effects on redox potential and quantity and quality of DOM. Phenolics were generally of higher molecular weight and more oxidized with sedges in lowered WTs. Altered DOM character included changes in dissolved nitrogen (N), with higher N:[phenolics] with higher E4:E6 (absorbance ratio λ = 465:665) DOM in the lowered WT and sedge PFG treatments. Conversely, biomolecular assignments to amino‐sugars were largely absent from low‐WT treatments. Low WT resulted in the creation of unique N compounds, which were more condensed (lower H:C), that changed with depth and PFG. The accumulation of oxidized compounds with low WT and in sedge rhizospheres could be very important pools of electron acceptors beneath the WT, and their mechanisms of formation are discussed. This work suggests the effects of changes in vegetation communities can be as great as WT position in directly and interactively mediating peat redox environment and the redox‐activity of DOM.
Plain Language Summary
Peatlands are important ecosystems in both the global carbon (C) cycle and the Earth's climate system owing to their ability to store vast quantities of C taken from the atmosphere. Peat C stays locked up in these ecosystems largely owing to cool and wet conditions, and as such, these C stores are vulnerable to release back to the atmosphere if the climate or water levels change. Water table level and plant species composition have a combined effect on C and nitrogen (N) cycling in peatlands. We manipulated both factors in an experimental setting composed of 24 large bins into which we put intact peatland miniecosystems. Sedges play a big role in producing N compounds below the peat surface, and this work suggests these compounds can actually be synthesized into larger, less accessible compounds. In addition, activities of sedge roots and other dominant plant communities (such as shrubs in the heath family of plants) may interact in the synthesis of oxidized, larger molecules. These molecules can allow microbes to continue to decompose peat even in the absence of oxygen. This could increase the release of greenhouse gas carbon dioxide to the atmosphere, while reducing inputs of the stronger greenhouse gas methane.
Key Points
Changes in vegetation and water table position directly and interactively mediate peat redox environment and the redox‐activity of DOM
Phenolic character consisted of increased molecular weight in more oxidized peat occurring with a lower water table and presence of sedges
Plant functional groups have stratified effects on unique compounds, with more aromatics accumulating in mixed species rhizospheres