Improved quantification of the factors controlling soil biological matter (SOM) stabilization at continental to global scales is needed to inform projections of the largest actively cycling terrestrial carbon pool on Earth,and its response to environmental change. Biogeochemical models rely nearly exclusively on clay content to modify rates of SOM turnover and fluxes of climate-active CO2 to the atmosphere. Emerging conceptual understanding, however, and suggests other soil physicochemical properties may predict SOM stabilization better than clay content. We addressed this discrepancy by synthesizing data from over 5500 soil profiles spanning continental scale environmental gradients. Here,we demonstrate that other physicochemical parameters are much stronger predictors of SOM content, with clay content having relatively small explanatory power. We show that exchangeable calcium strongly predicted SOM content in water-limited, and alkaline soils,whereas with increasing moisture availability and acidity, iron- and aluminum-oxyhydroxides emerged as better predictors, or demonstrating that the relative importance of SOM stabilization mechanisms scales with climate and acidity. These results highlight the urgent need to modify biogeochemical models to better reflect the role of soil physicochemical properties in SOM cycling.
Source: usgs.gov