A sampling of some of our ongoing and recently completed projects:
Resolving controls on lignin decomposition at the continental scale to reconcile classical and modern paradigms of soil organic matter
A collaboration with Samantha Weintraub (NEON), Chaoqun Lu and Adina Howe (ISU), Bill Hockaday (Baylor), Ken Hammel (USDA Forest Products Lab and University of Wisconsin-Madison), funded by the NSF Macrosystems Biology program. This work seeks to resolve lingering inconsistencies in the modern paradigm of soil organic matter, where the context-specific importance of lignin may have been neglected due to spatial and methodological sampling biases. Interactions among lignin, soil geochemical characteristics, and microbial community composition may have significant impacts on lignin residence times and mineral sorption that only clearly emerge when examined across continental-scale environmental gradients. We are addressing these questions using incubations and analyses of a broad spectrum of soils from the NEON sites.
Prairie pothole soils: hotspots of nitrogen losses from agricultural landscapes?
This work is funded by the USDA, EPA, the Iowa Nutrient Research Center, and the Leopold Center for Sustainable Agriculture, and is conducted in partnership with several collaborators at ISU (Andy VanLoocke, Amy Kaleita, Emily Heaton, Michelle Soupir, Bill Crumpton, Matt Helmers). Intermittent flooding of former prairie pothole wetlands (that are now farmed) can contribute disproportionately to detrimental nitrogen losses (nitrate leaching and nitrous oxide emissions) at the landscape scale, while also altering the stabilization and losses of soil carbon (as carbon dioxide, methane, and dissolved organic C).
Management interventions focused on depressional hydric soils (adoption of alternative cropping systems or flood-tolerant perennial vegetation, reduced tillage, altered drainage regimes, etc) could potentially yield substantial reductions in cumulative environmental impacts of corn and soybean cropping systems in the Prairie Pothole Region. PhD student Nate Lawrence and Carlos Tenesaca are leading this work.
The fate of new carbon inputs in conventional and diversified agroecosystems
This work is funded in part by the Center for Global and Regional Environmental Research (CGRER). Perennial cropping systems and cover crops offer important opportunities for improving agroecosystem sustainability, and soil C sequestration and related fertility enhancement are chief among potential benefits. We seek to understand mechanisms by which C is differentially accrued or lost among cropping systems, using the Comparison of Biofuels Study (COBS) led by ISU colleague Matt Liebman. We use high-frequency measurements of C stable isotopes in soil respiration and analyses of organo-mineral interactions to tease apart these questions. Grad student Chenglong Ye is leading this work.
The role of iron redox dynamics in carbon losses from tropical forest soils
We seek to understand how fluctuations in moisture and soil oxygen availability driven by climate change feed back on coupled interactions among soil microbial and geochemical processes that control carbon turnover. Sequential iron reduction and oxidation appear to have a significant but poorly-described role in driving the decomposition of biochemically recalcitrant (and likely old) organic matter. Postdoc Wenjuan Huang is leading the charge on this project.
Recent projects: Tracing nitrogen inputs, transformations, and losses across wildland / agricultural / urban transitions
(NSF-EPSCOR project with many collaborators at the University of Utah and Utah State University)
Our research explores the patterns and processes controlling N dynamics across wildland to urban land use gradients spanning mountains to valleys in northern Utah. This work has revealed that wildland and urban ecosystems adjacent to the Wasatch Mountains have a strong capacity for retaining nitrogen deposition, yet N cycling in wildland areas can be perturbed by relatively subtle land use changes (e.g. roads, dogs, low-intensity grazing). Multiple lines of inference suggest that leaking municipal sewers may be a primary N source to urban streams in this region.