Abstract
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 is largely comprised 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, we 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 meters 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 CO2 and 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 non-significant. Contrary to expectations, N and P additions did not increase CO2 and CH4 production, indicating that nutrient availability was not a primary constraint in microbial decomposition of deep peat. Our findings indicate that temperature is a key factor limiting the decomposition of deep peat, however other factors such as the availability of O2 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.
Highlights
Owing to their cool, saturated conditions, northern peatlands serve as an extensive carbon (C) sink storing approximately one third of the world’s terrestrial C [1,2,3]
We found that the mineralization of deep peat C to CO2 and CH4 was largely controlled by functional, rather than structural, responses of the microbial community to increased temperature
Elevated temperature increased production of both CO2 and CH4, Constraints on decomposition of deep peat as well as the ratio of CH4:CO2 produced. Despite these physiological responses of increased C mineralization, elevated temperature had a relatively minor influence on the microbial community composition. qPCR analyses showed both overall archaeal and methanogen population sizes decreased with elevated temperature, the size of the bacterial population showed no response
Summary
Owing to their cool, saturated conditions, northern peatlands serve as an extensive carbon (C) sink storing approximately one third of the world’s terrestrial C [1,2,3] In these systems, peat profiles accumulate largely undecomposed plant material to several meters deep representing thousands of years of C accumulation [4,5]. Warming trends are expected to be greatest at high latitudes [8] and there has been an increased effort to understand how C cycling processes in northern peatlands will respond to these predicted changes Much of this effort has focused on the acrotelm, the shallow peat that experiences a fluctuating water table, where it is expected that warmer and drier conditions will stimulate C mineralization [1,9,10,11]. Temperature-induced changes in microbial community composition or function in the catotelm layer could dramatically alter the C balance in these systems over time
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
