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PI-Submitted Research Highlights for
Terrestrial Ecosystem Science Program

Constraints on Microbial Communities, Decomposition, and Methane Production in Deep Peat Deposits

Christopher W. Schadt

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September 30, 2019

Temperature is among key factors constraining microbial processes in deep peat deposits.

The Science
This experiment tested the limitations that factors such as pH, nitrogen, and phosphorus may place on peat decomposition. Results showed the peat decomposition and microbial communities were indeed limited by temperature, more so than by nitrogen and phosphorous, but responses were slow to develop even under laboratory conditions.

The Impact
The effects of temperature on peat decomposition and methanogenesis in peatlands may occur over the long term rather than the short term. Other factors such as oxygen, iron, or carbon quality likely play additional roles in constraining peat decomposition responses to temperature.

Summary
Peatlands play outsized roles in the global carbon cycle. Despite occupying a rather small fraction of the terrestrial biosphere (~3%), these ecosystems account for roughly one-third of the global soil carbon pool. This carbon largely consists of undecomposed deposits of plant material (peat) that may be meters thick. The fate of this deep carbon stockpile with ongoing and future climate change is thus of great interest and has large potential to induce positive feedback to climate warming. Recent in situ warming of an ombrotrophic peatland indicated that the deep peat microbial communities and decomposition rates were resistant to elevated temperatures. In this experiment, researchers from Oak Ridge National Laboratory sought to understand how nutrient and pH limitations may interact with temperature to limit microbial activity and community composition. Anaerobic microcosms of peat collected from 1.5 to 2 m in depth were incubated at 6°C and 15°C with elevated pH, nitrogen (NH4Cl), and/or phosphorus (KH2PO4) in a full factorial design. The production of carbon dioxide (CO2) and methane (CH4) was significantly greater in microcosms incubated at 15°C, although the structure of the microbial community did not differ between the two temperatures. Increasing the pH from ~3.5 to ~5.5 altered microbial community structure; however, increases in CH4 production were not significant. Contrary to expectations, nitrogen and phosphorus additions did not increase CO2 and CH4 production, indicating that nutrient availability was not a primary constraint in microbial decomposition of deep peat. These findings indicate that temperature is a key factor limiting the decomposition of deep peat, but other factors such as the availability of oxygen or alternative electron donors and high concentrations of phenolic compounds may also exert constraints.  Continued experimental peat warming studies will be necessary to assess if the deep peat carbon bank is susceptible to increased temperatures over the longer time scales.

Contacts
BER Program Manager
Daniel Stover
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Earth and Environmental Systems Sciences Division (SC-33.1)
Environmental System Science
daniel.stover@science.doe.gov

Principal Investigator
Christopher W. Schadt, Senior Scientist
Oak Ridge National Laboratory
Oak Ridge, TN
schadtcw@ornl.gov

Funding
This work was supported by the Office of Biological and Environmental Research (BER), within the U.S. Department of Energy (DOE) Office of Science, as part of the Terrestrial Ecosystem Science (TES) Science Focus Area (SFA), and the Spruce and Peatland Responses Under Changing Environments (SPRUCE) project (http://mnspruce.ornl.gov).

Publications
Kluber, L., et al. “Constraints on microbial communities, decomposition and methane production in deep peat deposits.” PLOS ONE 15(2), e0223744 (2020). [DOI:10.1371/journal.pone.0223744].

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