The biogeochemistry of peatlands: linking nutrients, stoichiometry and greenhouse gases

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The overall objective of my research program is to establish the relationships between soils and the environment, under natural and disturbed conditions. I have focused much of my attention on peatlands which cover over 1 million km2 in Canada and play an important role in the global carbon (C) cycle with feedbacks to climate change. This involves field and laboratory studies of key processes in peatlands, with a strong integration with the development and application of models. Many peatlands have developed under conditions of limited nutrient availability but there have been increases in the atmospheric deposition of N and P, enhancing nutrient availability. Part of my research here examines the effect of increased N and P availability on the functioning of peatlands, including changes in vegetation, hydrology, greenhouse gas exchange and C sequestration. Critical to this are the relationships between C, N, P and other nutrients, in vegetation and peat, as part of ecological stoichiometry. In this proposal, I outline three objectives to contribute to answering these issues.***The effect of nutrient addition on the functioning of an ombrotrophic bog I plan to continue a long-term study of increased N addition, simulating increased atmospheric deposition, to the Mer Bleue peatland. As the longest running peatland nutrient addition experiment in North America, we have observed changes in plant and microbial communities, resulting in a weaker CO2 sink and increases in CH4 emission. Many of the changes did not appear for several years, highlighting the importance of long-term experiments. The bog will continue to be fertilized to 2024 and measurements will be made of CO2 exchange and CH4 and N2O emissions as well as using 13CO2 and 14CO2 to determine the proportion of root and peat respiration (one PhD student).***The ecological stoichiometry of peatlands My work has identified differences in C:N:P nutrient maintenance among plant species, which may explain their relative ability to withstand nutrient addition and in a Redfield Ratio' in Canadian forests and peatlands. I will test whether these relationships are more broadly applicable, using a large data base of plant and peat nutrient content in New Zealand and deep peat cores, formed under different conditions than Canadian peatlands (one MSc student).***CH4 emission by trees along dry-wet gradients Although much work has been done on exchange of CH4 between soils and the atmosphere, there is now evidence that trees can be significant contributors to CH4 emission. I propose to measure the role of tree stem emission of CH4 along two transects representing a sequence from well drained to peat soils at a bog and a swamp, with common tree species along the gradient. Fluxes of CH4 from tree stem and soil surface will be related to environmental variables and spatially extrapolated to test whether we need to take into account the role of trees (one PhD student).**