Pacific Northwest National Laboratory, US

Vanessa Bailey is a laboratory fellow at PNNL. Her research focuses on understanding the integrated microbial, chemical, and physical system that comprise soils. To achieve this understanding, she studies how water dynamics within soil pores leads to changes in soil carbon chemistry at pore-, core-, and field scales. This helps resolve the bioavailability of chemically and spatially defined soil carbon to soil microorganisms. Soil microbial communities are a key buffer system against perturbations to the earth from climate change, pollution, and disturbance. Bailey and colleagues have conducted research showing, for example, that the rate at which microbes are transferring carbon from soil to the atmosphere has increased over a 25-year time period. She also manages one of the Department of Energy’s largest coastal research projects, COMPASS, where she is leading efforts to understand the transformations and exchange of carbon and nutrients across the interface between land and sea.

Day 1 – Session 2: Exploring Interactions Within Phytobiomes

Physical controls on microbial carbon cycling in soils


Soil structure, soil water, and soil microbiology interlink to regulate the soil carbon cycle; carbon cycle feedbacks to the Earth system result from the destabilization of soil carbon. Destabilization includes processes that occur along a spectrum through which carbon shifts from a “protected” state to an “available” state where it can be mineralized by microbes to gaseous or soluble forms that are then lost from the soil.  The physical structure of soil – aggregates and pores – partially govern these shifts. For example, soil pores comprise the habitat for soil microbes, the flow paths for resource transport in the aqueous phase, and pore water is the reagent within which biogeochemical transformations occur. We combine advanced techniques for molecular characterization of soil carbon with tomography and sequencing to reveal where in the soil matrix carbon persists, and in what forms. We have found little evidence for chemical recalcitrance as a carbon protection mechanism. We have imposed extreme water cycles, from drought through flood, and found that moisture history is a strong control on the forms of carbon in soil, where they are located, and how they contribute to CO2 emitted through heterotrophic respiration. Yet, we find these patterns are expressed differently in different soils and we hypothesize that water and soil structure may explain some of these differences. By considering different physical, chemical, and biological controls as processes that contribute to soil C destabilization, we can inform more accurate and robust predictions of soil C cycling in a changing environment.