Plant functional group identity influences short-term peatland ecosystem carbon flux: evidence from a plant removal experiment

1. Northern hemisphere peatlands are globally important stores of organic soil carbon. We examined effects of plant functional group identity on short-term carbon (C) flux in an ombrotrophic peatland in northern England, UK, by selectively removing one of each of the three dominant plant functional groups (ericoid dwarf-shrubs, graminoids and bryophytes). Carbon dynamics were quantified by a combination of CO2 flux measurements and (CO2)-C-13 stable isotope pulse labelling approaches. 2. Significant effects of plant functional group removals on CO2 fluxes and tracer C-13 uptake and turnover were detected. Removal of ericoid dwarf- shrubs had the greatest influence on gross CO2 flux, increasing rates of respiration and photosynthesis by > 200% relative to the undisturbed control. After pulse labelling with (CO2)-C-13, we found that turnover of recent photosynthate, measured as respired (CO2)-C-13 was also greatest in the absence of dwarf- shrubs. 3. Analysis of C-13 tracer enrichment in leaf tissues from all plant removal treatments showed that the rate of fixation of (CO2)-C-13 and turnover of C-13 labelled photosynthate in leaf tissue was greatest in graminoids and lowest in bryophytes. Furthermore, graminoid leaf C-13 enrichment was greatest when growing in the absence of dwarf-shrubs, suggesting that the presence of dwarf- shrubs reduced the photosynthetic activity of graminoids. 4. We conclude that plant functional groups differentially influence the uptake and short-term flux of carbon in peatlands, suggesting that changes in the functional composition of vegetation resulting from global change have the potential to alter short-term patterns of carbon exchange in peatland.