The effect of disturbance on the biogeochemical cycling of carbon in northern forest soils

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Soil organic matter is the largest terrestrial reservoir of organic carbon (OC) and its decomposition is responsible for the annual release of an estimated 75 Pg carbon (C) into the atmosphere as carbon dioxide (CO2). Over 70% of these emissions are derived from a small pool (<1% of total C) of recently incorporated (<1 yr) organic matter, with the remaining emissions being derived from a more stable pool of soil organic carbon (SOC). This stable pool of SOC is slower to decompose because it is protected from decomposition physically, chemically and/or biologically. Though we have a reasonable understanding of how the small, fast cycling pool of SOC responds to environmental change, our knowledge of the process of stabilization/destabilization of the more stable pool of SOC is not as well developed. As climate changes, forest fires are expected to become more frequent in northern forests and opportunities for agricultural expansion are emerging with increases in growing degree days in northern regions. In tandem, there has been increasing interest in bioenergy generation using the combustion of biomass which generates wood ash that is alkaline and may be used as a soil amendment to improve site productivity. Fires and land management, alongside changes in climate, alter the soil environment physically, chemically, and biologically which may lead to changes in the pool(s) of "stable" carbon. Over the next five years my research program will investigate the effects of ash addition on the transformation and transport of SOC with the specific objectives of: 1. quantifying the role of Ca, alongside Fe and Al, on stabilization of SOC in acidic northern soils, 2. assessing the potential for increases in pH and Ca to enhance the stabilization capacity of mineral associated organic carbon in acidic soils, and 3. determining if the amount of ash added affects the transformation and transport of SOC deeper into the soil profile. Meeting the short-term objectives of my program will contribute to my career goals of 1. Improving our understanding of the effects of environmental changes on the biogeochemical cycling of SOC in northern soils and 2. Advancing the use of C isotopes and SOC fractionation techniques in biogeochemical investigations. These objectives will be met through concurrent student led projects.