Collaborative Research: Long-term changes in peatland C fluxes and the interactive roles of soil climate, vegetation, and redox supply in governing anaerobic microbial activity

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Northern peatlands store a large proportion (30%) of the world's soil carbon, and given their predominance at high latitudes are expected to experience warming at twice the global rate. Warming of peatlands, therefore, has high potential to create strong feedbacks to global climate if it causes accelerated rates of decomposition that result in the release of this carbon to the atmosphere. Our current view of carbon cycling in peatlands suggests that the majority of decomposition occurs in the thin, oxygen-rich peat layer above the water table. Once carbon is transferred to deeper, saturated peat layers, decomposition rates of carbon are thought to be negligible due to cold temperatures and low-oxygen conditions that inhibit decomposition. Peat soil carbon below the water table can, however, be decomposed by microbes using a variety of biochemical processes that don't rely on free oxygen, but are energetically less efficient. These alternative metabolic pathways can result in the production of methane (CH4), a trace gas with much higher greenhouse warming potential than carbon dioxide (CO2). Thus, the position of the water table has traditionally been used as a predictor of overall decomposition rates and methane production in peatlands. However, preliminary results from an Alaskan peatland water-table manipulation experiment (the Alaska Peatland Experiment, or APEX) suggest that decomposition and resulting CO2 production may be higher in deeper peat layers than previously thought. The goals of this research are to investigate the factors driving decomposition of carbon in deep peat layers, and to use this information to benefit society by improving future projections of the impact of peatlands on global climate. This study will also provide valuable opportunities for the training of undergraduate and graduate students, and to educate school children on the drivers and impacts of climate change through collaboration with the Schoolyard LTER program. Over the past 8 years, research on APEX has examined the role of changing soil climate and vegetation on peatland carbon cycling through monitoring changes in soil moisture and temperature, plant composition and biomass, and ecosystem CO2 and CH4 fluxes. The experiment includes a factorial design of water table treatments (including lowering the water table to simulate drying, and raising the water table to simulate flooding) and surface soil warming in an Alaskan fen. This research has revealed gaps in our understanding of microbial decomposition processes in peatlands, and provides the context for the hypotheses being tested in this project. In particular, previous work suggests different plant functional types interact with water table in determining aerobic and anaerobic peat decomposition. In addition, variation in litter chemistry between plant functional types is hypothesized to be a major driver of decomposition rates in peatlands. Collectively, these factors suggest that changes in vegetation exert significant control over anaerobic decomposition processes in peatlands, but to date these effects have not been studied adequately, in part because it is difficult methodologically to separate vegetation from hydrologic controls on decomposition. New experiments being conducted in this project are designed to provide mechanistic insights into a suite of factors, including the role of vegetation, that control stabilization of peatland carbon.