Abstract: Peatland ecosystems, often dominated by Sphagnum mosses, cover 3.5 % of the earth's land surface and store 455 million metric tons of carbon as partially decayed organic matter, or peat. Peat accumulates when net primary production (NPP: plant photosynthetic CO2 fixation minus plant respiration) exceeds decomposition of dead plant remains and peat (releasing CO2 and CH4 to the atmosphere). Largely located today in the boreal regions of the northern hemisphere, peatland ecosystems were largely absent at the time of most recent glaciation. Thus, over the past 6,000-10,000 years, peatlands have represented a major global net sink for atmospheric CO2. Modern global climate models predict substantial warming of the boreal regions of the northern hemisphere by the year 2050. How predicted climate change will affect C cycling in boreal peatlands is a key piece of the global climate change puzzle.

Rates of carbon sequestration in peatlands over the past 200 years can be quantified using lead isotope dating of intact field-collected peat cores. Present-day C cycling can be assessed directly through measurement of NPP, decomposition rates, and/or net CO2/CH4 exchange across peatland/atmosphere boundaries. To predict future responses, however, modeling approaches are needed. Models developed in our laboratory suggest that if climate change results in only slight decreases in NPP and/or slight increases in decomposition rates, peatland ecosystems may shift from functioning as net global sinks for atmospheric C to net global sources, and hence could provide a positive feedback on ongoing climate change.