Soil is a composite of minerals, organic matter, water, and air. The structural arrangement of these components into pore networks define where different biogeochemical processes can take place. The distribution of such processes across a volume of soil is therefore inherently heterogeneous. Recent literature has shown that soils that are nominally oxic can contain smaller anoxic regions in which biogeochemistry markedly differs from the surrounding oxic soil volume. These regions form where the supply of oxygen by diffusion outpaces oxygen demand by respiring microbial communities. The resulting shift in respiration pathway from aerobic to anaerobic causes a slowdown in organic carbon mineralization and, depending on the respiration pathway, a buildup of reduced metal species. Together with researchers at University of Lausanne, Stanford University and the SLAC National Accelerator Laboratory, we are testing for soil redox heterogeneities in soil aggregates from different soil horizons on variable bedrock at the Stanford Dish area. We are assessing potential differences in soil redox state and active microbial genes between the inside and outside of soil aggregates and combine these analyses with synchrotron-based imaging to assess the spatial arrangement of reduced metal species in our aggregates.
People: Meret Aeppli
Collaborators: Emily Lacroix, Scott Fendorf, Anna Gomes, Vincent Noël, Cherie DeVore