Boreal bog Sphagnum refixes soil-produced and respired 14CO2

Research on peatland C cycling has generally ignored refixation, i.e., the photosynthetic fixation of soil-produced or respired CO2. We quantified refixation in a boreal bog by transplanting groups of living nonradioactive Sphagnum fuscum (5 cm length, 4 cm diameter) into N-, P-, and S-fertilized field plots that had been radioactively labeled by exposure to (CO2)-C-14, and analyzing transplants retrieved at 2, 30, and 90 days post-labeling for C-14 activity. Sphagnum transplanted into plots that received both N and S had greater refixed C-14 activities (Bq g(-1)) than control plot transplants. Sphagnum capitulum (top 1 cm), 1-2 cm, and 2-5 cm sections behaved similarly with the capitula having the highest refuted C-14 activity and the 2-5 cm section having the lowest; differences between sections became more accentuated over time. Extrapolated to a m(2) basis, transplanted Sphagnum refixed 3.5-5.4% of the total C-14 initially incorporated into the living vegetation and top 10 cm of peat during labeling. Refixation may be an important pathway for C cycling within peatlands, potentially capturing significant proportions of peat-produced or respired CO2 before it escapes to the atmosphere.