Pedogenesis and Carbon Fluxes Across a Lithosequence of Forest Soils.

Carbon is sequestered in soils both through preservation of organic matter and the production of carbonates during silicate weathering. Concerns over global warming have increased interest in modeling fluxes of C in soils, however variation in the mechanisms of soil C sequestration as a function of parent material remains poorly understood. We sampled a lithosequence of four parent materials (rhyolite, granite, basalt, limestone) under Pinus ponderosa to examine variation in organic C preservation and carbonate flux as a function of parent material. Three soil profiles were examined on each parent material and analyzed by a combination of qualitative and quantitative X-ray diffraction, thermogravimetric analyses (TG-DTA), total elemental analysis, pH, selective dissolution, and organic C content. Pedogenesis and soil C cycling was quantified using a novel coupling of quantitative mineralogical data and geochemical mass balance techniques. Both organic and inorganic C cycling varied significantly among soils of different parent materials and was related to directly to variation in mineral weathering and transformation. The flux of weathering produced was significantly higher in soils derived from basalt than in the other soils examined, while soil organic C contents were highest in soils derived from rhyolite. Results strongly suggest that parent material should be taken into account when estimating both organic and inorganic C fluxes from soils.