Deep under cover: a pedological perspective on soil carbon

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Soils are the largest terrestrial carbon storehouse on Earth. Canadian soils alone contain more than 10% of global soil carbon stocks. As soils contain more carbon than all plants and the atmosphere combined, even small changes in soil carbon stocks can significantly alter the global carbon cycle. Carbon storage in soils reflects the influence of several environmental factors, ranging from topography (slope position) at the local scale, to interlinked variations in parent geological material, climate, and vegetation at the regional to continental scale. What remains unclear is how these natural environmental variations impact the accrual pathways and persistence of soil carbon. Further, a broad understanding of soil carbon response to anthropogenic changes, such as altered rain events and plant root growth, does not exist. My research program will focus on three key components of carbon in Canadian soils: 1.Subsoil organic carbon: More than half of total soil carbon is located below 30 cm. For this first objective, I will quantify net carbon balances in key soil types across Canada, with the overarching hypothesis that different pedogenic processes across soil types control both input pathways at depth and subsoil carbon persistence. At the local scale, I will determine how total carbon stocks increase but carbon persistence decreases with decreasing drainage. 2.Inorganic carbon: Carbonates (inorganic carbon) are the dominant form of carbon in many soils from Western Canada. How this important soil carbon pool will eventually fare under global climate change has not been ascertained. My second objective will be to assess how shifting patterns in drainage and below-ground plant productivity alter the contribution of inorganic carbon to soil carbon balances. 3.Soil fauna: Climate change and land-use changes may trigger biological invasions. In particular, the ongoing invasion of non-native earthworms into Canadian soils is having a profound impact on their carbon dynamics. Here I will investigate how the net carbon balance in earthworm-invaded soils varies among key representative soil types. Whether soils act as carbon sinks or sources depends on the net balance between carbon entering (inputs) and leaving (outputs) the soil. In many cases, measuring the net balance between soil carbon inputs and outputs is complex, but assessments can be greatly improved by taking advantage of natural variation in stable carbon isotopes, or by tracking carbon fluxes using artificial labeling. Combining a sound pedological field approach and experiments under controlled-laboratory conditions should provide unprecedented insight into the processes of carbon persistence in soils. Overall, the goal of this research program is to establish the foundational scientific knowledge required to improve predictive soil carbon models, and to create meaningful and sustainable climate change adaptation strategies that can be tailored to different soil types.