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 biogeochemical cycling. These efforts have been funded by the National Science Foundation, NASA, the US Forest Service, USDA-NIFA, and the Department of Energy. 

Two key foci are 1) the influence of climate change and historic land cover on biogeochemical fluxes 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 and sculpt the soil environment to govern larger-scale ecosystem modulation of climate. 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 profile characteristics and their influence on landscape-scale, biosphere-atmosphere-hydrosphere linkages that govern climate. 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 roots, and understanding how they link to soil organic C persistence. This work is funded by NSF grant EAR-2012633.

Signals in the Soils

These projects explore how biotic and abiotic forces can combine to influence soil aggregate formation and collapse, how that links to soil organic C preservation and associated soil-climate feedbacks, and how we can offer climate models more well-constrained input parameters to project future water fluxes. The project is lead by Dr. Pamela Sullivan at Oregon State University, and the Billings Lab represents the KU portion of the project. This work is funded by NSF grants EAR-2026874 and EAR-2034232, with additional funding from the USDA.

Plant Biodiversity as a Driver of Soil Organic C

Post-doctoral researcher Dr. Laura Podzikowski is funded via a USDA post-doc fellowship to explore how plant biodiversity (both at the species level and the plant functional type) can influence the fluxes that govern SOC pools. This work takes place at the KU Field Station, leveraging years-long precipitation shelters that manipulate moisture availability in plots of varying plant diversity levels. 

Linking Feedbacks Between Ecosystem Function and Microbiome Structure and Function to Variation in Precipitation Regime

Working with researchers across Kansas, this project investigated how precipitation regime and land use can influence soil biogeochemical processes.  We are especially interested in altered rooting depths imposed by land cover and how this modifies soil deep within the profile.  We specifically investigated how organic matter dynamics are driven by interactions among rooting depth, rhizosphere microbes, and precipitation, working in native, regenerating, and agricultural systems. The work was funded by a NSF EPSCoR Research Infrastructure Improvement award, Microbiomes of Aquatic, Plant, and Soil Systems across Kansas (MAPS). Manuscripts continue to emerge as we work with these datasets.

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 organic carbon and gas fluxes in recently disturbed landscapes, recovering forests, and old-growth reference sites. The work puts current roots and soil carbon 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.