Research
Research in my lab is diverse, working across scales, taxa, and ecosystems. Historically, we have explored how perturbations like drought, elevated CO2, and habitat fragmentation can influence above- and below-ground carbon and nitrogen cycling. These efforts have been funded by the National Science Foundation, NASA, and the Department of Energy.
Two key foci are 1) the influence of climate change and historic land cover on nutrient and carbon flows through soils, microbes, and vegetation, and 2) vegetation and microbial abilities to structure soil profiles via their efforts to acquire resources. We explore these and related questions in temperate and boreal forests and mid-western grasslands. We are especially interested in how roots interact with the soil environment to govern larger-scale fluxes of elements. Much of our work relies on stable isotopes and the isotopic fingerprints imparted by biological and chemical fluxes on ecosystem pools of organic matter (e.g., soil organic matter, microbes, tree-rings).
We work with KU’s W.M. Keck Paleoenvironmental and Environmental Stable Isotope Laboratory, employ cavity ring down spectroscopy for stable isotopic signatures of CO2 and CH4, and use 14C to explore the persistence of soil organic carbon stocks. We also leverage soil microbial sequencing data to infer dominant biogeochemical environments throughout soil profiles.
Ongoing Research
Frontier Research in Earth Sciences
For this cross-disciplinary project we investigate the relative importance of top-down (i.e., roots and microbes; climate) vs. bottom-up (i.e., bedrock characteristics and mineralogy) controls on soil structure and the resulting flows of water, solutes, and gases through and across landscapes. The team is composed of investigators from Oregon State University, the University of California Riverside, Kansas State University, Colorado School of Mines and Technology, Penn State University, and Boise State University and is led by Dr. Pamela Sullivan at Oregon State University. This work is funded by NSF grant EAR-2121639.
The Critical Zone Network’s Geomicrobiology Project
Lead by Dr. Emma Aronson at the University of California Riverside, this project explores how microbial identity and functioning varies with land use, lithology, vegetative cover, and depth. We are especially interested in depth distributions of microbial and biogeochemical fluxes, and understanding how they link to soil organic C persistence. This work is funded by NSF grant EAR-2012633.
Signals in the Soils
We have two on-going SitS projects in the lab. The first works to develop the parameterization needed for models at the pedon, hillslope, watershed, and continental scale that attempt to examine how changing soil structure can influence water flows, soil weathering, biogeochemical fluxes, and soil-climate feedbacks. The second project explores how biotic and abiotic forces can combine to influence soil aggregate formation and collapse, and how that links to soil organic C preservation and decay, soil pore formation, and associated soil-climate feedbacks. This project also strives to develop accurate input parameters for models at a diversity of scales. Both of these projects are lead by Dr. Pamela Sullivan at Oregon State University. This work is funded by NSF grants EAR-2026874 and EAR-2034232, with additional funding from the USDA.
Linking Feedbacks Between Ecosystem Function and Microbiome Structure and Function to Variation in Precipitation Regime
Working with researchers across Kansas, we are investigating how precipitation regime and land use can influence soil biogeochemical processes that drive soil profile retention of organic and inorganic resources. We are especially interested in altered rooting depths imposed by land cover, how this modifies soil structure deep within the profile, and nutrient dynamics. We specifically explore investigate how organic matter dynamics are driven by interactions among rooting depth, rhizosphere microbes, and precipitation, working in native, regenerating, and agricultural systems. The work is funded by a NSF EPSCoR Research Infrastructure Improvement award, Microbiomes of Aquatic, Plant, and Soil Systems across Kansas (MAPS).
The Calhoun Critical Zone Observatory
A team of investigators from multiple universities and led by Duke University’s Dr. Daniel Richter developed the NSF-funded Critical Zone Observatory at the Calhoun Experimental Forest in Union, South Carolina. As of late 2021, funding ceased. However, we continue to analyze data obtained from these efforts, and our knowledge continues to develop. We study the extent to which former land use continues to influence current ecosystem functioning, integrating both human and natural forcings. The Billings lab leads KU’s contribution to the project. We focus on biogeochemical legacies of disturbance evident in Calhoun’s recovering forests by contrasting root abundance and subsoil carbon and nutrient fluxes in recently disturbed landscapes, recovering forests, and old-growth reference sites. The work puts current roots and soil carbon and nutrient fluxes into a context of centuries-old ecological change and contemporary climate change. Our efforts are relevant around the globe, given the intensity of agricultural land use, associated accelerated erosion, and the frequency of abandonment in many regions. This work was funded by NSF grant EAR-1331846.
The Influence of Climate Change on Soil Organic Carbon Decomposition and Formation in Boreal Forests
Given the large reservoir of soil organic carbon compounds in boreal forests, it is important to learn about the microbial processes governing their transformations. In collaboration with scientists in the Canadian Forest Service and Dr. Susan Ziegler at Memorial University of Newfoundland, we are exploring the transformations of carboniferous compounds in soil profiles along a climate transect of balsam fir forests in Newfoundland. We work along the Newfoundland Labrador Boreal Ecosystem Latitudinal Transect (NL-BELT), seeking to understand how climate influences the formation and transformations of soil organic carbon compounds. Publications from this work are available in Soil Biology and Biochemistry, Biogeochemistry, Frontiers in Earth Science, Soil, and Journal of Geophysical Research – Biogeosciences. This work was funded by the Humber River Basin Project, a consortium of funding agencies in Canada including the Canadian Forest Service and Newfoundland and Labrador’s Forestry Office.
Modeling Soil Erosion as a Carbon Source or Sink
Recent studies indicate that soil erosion may serve as a net sink for carbon, though this is an unresolved controversy in the literature. We have developed a user-friendly, spreadsheet-based model that permits investigators to examine an eroding soil profile of interest and determine the extent to which its erosion results in a net atmospheric carbon source or sink. Rather than asserting that erosion serves as either a net carbon source or sink, the model serves as a tool to assess which parameters are critical determinants of the net carbon flux into or out of an eroding profile. The model was developed in collaboration with Dr. Robert Buddemeier at the Kansas Geological Survey. Those interested in exploring the model can download it on the ‘Modeling erosion and CO2‘ tab, and read about it in our 2010 article A simple method for estimating the influence of eroding soil profiles on atmospheric CO2. in Global Biogeochemical Cycles. Our 2019 publication Distinct Contributions of Eroding and Depositional Profiles to Land-Atmosphere CO2 Exchange in Two Contrasting Forests in Frontiers in Earth Science follows up on this idea by integrating a depositional module to the model. We have transformed the model into R to help future-proof it.