Controls on Soil Organic Carbon Partitioning and Stabilization in the California Sierra Nevada

There is a critical need to quantify the role of soil mineral composition on organic carbon (C) stabilization in forest soils. Here, we address this need by studying a matrix of forest ecosystems and soil parent materials with the objective of quantifying controls on the physical partitioning and residence time of soil organic carbon. We sampled soil profiles across a climate gradient on the western slope of the California Sierra Nevada, focusing on three distinct forest ecosystems dominated by ponderosa pine, white fir, or red fir, on three igneous parent materials that included granite, andesite, and basalt. Results indicated that short-range order mineral phases were the dominant factors accounting for the variation in soil carbon content and residence time. The results further suggested an interaction between ecosystem fire regime and the degree of soil weathering on the partitioning, chemical composition, and residence time of C in density separated soil physical fractions. These results suggest a link between the degree of soil weathering and C storage capacity, with a greater divergence in storage capacity and residence time in the Inceptisols, Entisols, and Andisols of the white fir and red fir ecosystems relative to minimal variation in the highly weathered Ultisols and Alfisols of the ponderosa pine ecosystem.