Controls on Autotrophic and Heterotrophic Respiration in an Ombrotrophic Bog

Abstract:

Northern peatlands are considered globally significant carbon stores, but the sink strength may vary from year-to-year due to variations in weather conditions. Peatlands cover roughly 12% of Canada’s terrestrial surface, thus future changes in climate (or land use) could have an impact on Canada’s overall greenhouse gas emissions. Models can project the sensitivity of peatland carbon balance components to climate and land-use changes. However, most models only crudely partition ecosystem respiration into its autotrophic (AR; respiration by plant parts) and heterotrophic (HR; respiration by microbial bacteria in the soil) components. This partitioning approach may lead to erroneous estimates if a change favours one form of respiration over another and alters allocations of carbon to labile pools with different turnover rates. Additionally, obtaining direct measurements is essential to explaining the temporal and spatial dynamics of respiration. The objective of this study is thus, to determine the factors that drive the spatial and temporal variability in respiration and its autotrophic and heterotrophic components at Mer Bleue, an ombrotrophic bog. Direct plot level measurements (manual chamber methods) were used to partition respiration, and the controls on respiration were explored by measuring a variety of environmental variables. Results show AR is driven primarily by water table position and HR by air and soil temperatures, with the shrub species showing a higher variability in respiration than the sedge species. Furthermore, the role of belowground processes (e.g. cycling of nutrients and root dynamics) was explored through root exudate, nutrient and stable isotope analyses. These findings seem to support the respiration results and will be explored further. This project will improve our understanding of peatland carbon cycling as well as improve the parameterization of current peatland models.