| Peatland-forest ecotones are critical locations for monitoring potential impacts of high latitude warming, which could cause northern peatlands to become sources of carbon (C) to the atmosphere. We characterized the soils, hydrology, and forest structure of a peatland-forest ecotone in southeastern Alaska. We measured soil properties that affect C storage and C loss, including N availability. In the forest interior, conifers generally grew on mineral soils, but at the forest edge, they also grew on Cryofibrists and Cryohemists, soils with high soil organic C (SOC) to 100 cm (57 kg m−2) that is significantly greater than the SOC of adjacent forested, non-Histosol pedons. Soil respiration rates (SRR) at peatlandforest edges (0.08 g CO 2-C m−2 h−1) were threefold lower than forest rates and did not differ significantly from peatland rates. A model incorporating water level, ecotone station, and soil water balance explained >50% of the variance in SRR. On a landscape basis, soil temperature was not a significant predictor of SRR, in part because all but forest interior stations were very poorly drained.; More than 90% of the variance in N mineralized during 28-day field incubations could be explained by these variables: C:N ratio, basal area, and a combination of water levels and soil temperatures (WLT) and the interaction of WLT with basal area. Laboratory and field mineralization results were not consistent. If N availability is a function of total N, N availability at peatland-forest edges will be sufficient to support expansion of forests. Our conceptual model suggests that if additional forest expansion and warmer summers enhance drainage of these edge soils and stimulate SRR to forest-like levels, 23 kg C m −2 could ultimately be mineralized from these extensive peatland-forest boundaries. Afforestation of peatland margins under this scenario could represent a transient positive feedback to rising atmospheric CO2 levels. |
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