Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Biology

Supervisor

Branfireun, Brian A.

Abstract

Northern peatlands are important long-term carbon (C) sinks with one-third of northern hemisphere soil organic carbon being stored there. Cool and wet environments at higher latitudes promote C accumulation in northern peatlands by limiting the C loss from decomposition. Northern latitudes are anticipated to experience disproportionately faster climate warming in the future, putting the vast C stores in northern peatlands at risk. There is a concern that northern peatlands are becoming net C sources and further accelerate climate warming. Using both laboratory and field experiments, this doctoral research aimed to explore the potential response of C cycling in northern peatlands to future climate change with the altered vegetation community, increased temperature and elevated atmospheric carbon dioxide (CO2).

Sedge-dominated peatlands are expected to become increasingly prevalent relative to Sphagnum-dominated peatlands under future climate change. By comparing C fluxes between a sedge-dominated intermediate fen and a Sphagnum-dominated poor fen, this doctoral study showed that northern peatlands would become a smaller CO2 sink by at least 16% but a larger methane (CH4) source by at least 15% if the ecosystem is shifted from Sphagnum to sedge-dominated. Additionally, with this vegetation shift, northern peatlands will exhibit a more biodegradable dissolved organic carbon pool; the constituent would have lower molecular weight and aromaticity.

The vegetation composition together with CO2 and CH4 fluxes remained stable in the Sphagnum-dominated poor fen under in situ passive warming. In the sedge-dominated intermediate fen, however, the net CH4 emission decreased by 11% under a moderate increase in temperature, owing to the greater CH4 oxidation with increased plant productivity. The elevated atmospheric CO2, together with more pronounced warming, concurrently increased aboveground plant productivity and belowground microbial decomposition, leaving the C sink function maintained in the sedge-dominated intermediate fen. Collectively, both warming and elevated CO2 could extend the growing season, which could potentially increase the CO2 uptake in northern peatlands.

Taken together, climate change can, both directly and indirectly, affect C fluxes in northern peatlands via altered vegetation community, vegetation biomass C allocation and the length of growing season. Vegetation-induced changes in C fluxes of northern peatlands should therefore be incorporated into atmosphere-ecosystem models to increase our ability in predicting the future climate.

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