Sources of C[O.sub.2] emission from a northern peatland: root respiration, exudation, and decomposition

Northern peatlands are substantial sinks of carbon (C), yet the sources of carbon dioxide (C[O.sub.2]) emitted from peatlands are largely unknown. Since the relationship between roots and peat in C cycling is important, vascular plants growing on the surface of peat deposits should influence C[O.sub.2] efflux from the peat surface and the overall C balance in peatlands. In our study, 30-cm peat cores were removed from an ombrotrophic bog in boreal,' continental western Canada. Surface vegetation in the cores remained intact and included a continuous bryophyte cover dominated by Sphagnum fuscum. In addition, some cores were collected such that either ericaceous shrubs (Ledum groenlandicum) or sedges (Eriophorum vaginatum) were present. We investigated how the presence of each vegetation type influenced soil respiration and the microbial mineralization of root exudates using a pulse [sup.14]C labeling of vegetation in the intact peat cores. The role of root biomass and root respiration in C[O.sub.2] emission and C allocation was quantified for each type of vegetation and compared through both measurement and modeling. Our results show that vascular plants contributed 35-57% of total C[O.sub.2] efflux from the peat surface, primarily derived from rhizosphere processes, including root respiration as well as microbial mineralization of root exudates. The mineralization of root exudates contributed 14-53 [micro]mol C-C[O.sub.2]*[m.sup.-2]*[d.sup.-1] (17-24% of total) to C[O.sub.2] efflux, depending on vegetation type and moisture conditions. The type of vegetation present did not influence the total amount of photosynthetic fixation over the course of the study, but did affect how C was allocated within and between both the aboveground and belowground components of the peat column. Key words: boreal; Canada; carbon balance; Eriophorum vaginatum; Ledum groenlandicum; ombrotrophic bog; peatlands; root exudation; Sphagnum fuscum.