Lawrence Livermore National Laboratory, US

Jennifer Pett-Ridge is a senior staff scientist and group leader at LLNL who uses the tools of systems biology and biogeochemistry to link, identity, and function in environmental microbial communities and pioneered the use of NanoSIMS isotopic imaging in the fields of microbial biology and soil biogeochemistry. As lead scientist of the LLNL Genomic Science Biofuels Scientific Focus Area (SFA) (2009–2018) and more recently the LLNL Soil Microbiome SFA, she leads multi-disciplinary teams that integrate biogeochemistry, stable isotope probing, NanoSIMS imaging, molecular microbial ecology, and computational modeling to understand biotic interactions and energy flow in microbial communities critical to soil nutrient cycling and sustainable biofuel production. Pett-Ridge is currently leading a county-level assessment of options for carbon dioxide removal in the USA. She is the group lead for the Environmental Isotope Systems group at LLNL and manages a large portfolio of DOE, NSF, NASA and foundation support. Pett-Ridge has published over 120 peer-review articles, has received a DOE Early Career award, Secretary of Energy Achievement Award, the Geochemical Society Endowed Biogeochemistry Medal, and the DOE Office of Science Ernest Orlando Lawrence Award.

Day 2 – Session 3: Soil and Rhizosphere

Life and Death in the Soil Microbiome: How Cross-Kingdom Interactions Shape the Fate and Persistence of Soil Carbon


Soil surrounding plant roots, the ‘rhizosphere’, is a nexus of biological activity. Stimulated by exudates and root decay, rhizosphere organisms (bacteria, archaea, fungi, fauna, and viruses) interact to move carbon from root tissue to surrounding soil, and ultimately regulate how soil carbon is stabilized. While the concepts of soil food webs are well established, a quantitative and mechanistic understanding of how networks of organisms control dynamics of soil organic matter (SOM) and respond to changing precipitation patterns is only recently emerging. While some bio-interactions may be mutually beneficial, many others are the proximal cause of microbial death and turnover, producing microbial ‘necromass’ that plays a critical role in the persistence of soil organic matter (SOM). Several factors mediate microbial population dynamics, including top-down pressure from phage and soil microfauna, and environmental shifts in moisture or resource availability.

I will present evidence from studies where cross-kingdom responses to environmental drivers have follow-on effects for soil carbon—including shifts in resource availability around roots, fungal-bacterial interactions, and microbial community successional shifts during a post-drought wet-up. In all of these systems, stable isotope probing (SIP) helps us assess the active microbial and viral community and quantitatively track plant-derived carbon. These studies suggest that cross-kingdom interactions, involving bacteria, fungi, archaea, protists, microfauna and viruses, shape carbon availability and loss pathways and are differentially influenced by both soil habitat (rhizosphere, detritusphere, bulk soil) and natural fluctuations in the physicochemical environment.