We are evaluating the long-term effects of prescribed fire on the abundance and stability of soil carbon. Understanding the effect of prescribed fire on soil carbon requires an examination of the complex interactions among fire, fuels, plants, and soil microbes that play out over decadal time scales. Our approach is to sample soils from fire experiments that have been ongoing for 20-70 years, and are distributed across major forest types of the eastern U.S. We will determine how fire alters the abundance and stability of soil carbon, by quantifying the amount of pyrogenic, mineral-associated and occluded carbon. We will also quantify changes in soil microbial community composition and function, including a focus on oxidative enzyme activity and melanized fungal hyphae because of their significance in mediating soil carbon stocks. The findings of our research have the potential to inform management decisions aimed at promoting the sustainability of eastern forests and their long-term potential to sequester carbon.

Co-PIs: Caitlin Hicks Pries and Rick Lankau and numerous fire-experiment collaborators.

Funding: USDA NIFA AFRI

Current biogeochemical frameworks primarily focus on the role of ectomycorrhizal and arbuscular mycorrhizal trees in carbon and nitrogen cycles. Ericaceous shrubs are common in the forest understory, but they associate with ericoid mycorrhizal (ErM) fungi, a mycorrhizal association that has received much less attention. The limited evidence available suggests that ErM shrubs have disproportionate effects on biogeochemistry relative to their biomass, but the mechanisms are unclear. Furthermore, ErM shrubs are expanding in temperate forests in response to a suite of biotic and abiotic disturbances, making it critical to understand their role in ecosystems. We are testing three mechanisms by which ericoid mycorrhizal shrubs affect soil carbon and nitrogen cycles: 1) high concentrations of leaf litter tannins, 2) nutrient mining of organic matter by ErM fungi and 3) high concentrations of melanin in ErM fungal necromass. We are using observational data from temperate forests and targeted isotopic tracing experiments to test these hypothesized mechanisms. We will use these data to parameterize and validate a soil biogeochemical model to project the consequences of expanding ErM shrub underestories on soil biogeochemistry. This project builds on our previous DOE-funded project focusing on tree mycorrhizal associations (see below).

Collaborators: Caitlin Hicks Pries, Rick Lankau and Ben Sulman.

Funding: DOE Environmental System Science

The mycorrhizal associations of forest trees drive soil carbon and nitrogen cycling. Forests dominated by ectomycorrhizal trees tend to have higher soil C:N and a higher proportion of particulate organic matter than those dominated by arbuscular mycorrhizal trees. However, the mechanisms behind these patterns are unclear. Across our forest sites in NH, IL, WI and GA, we find the expected patterns in soil organic matter only where forests are dominated by trees in the Pinaceae and Fagaceae, and the ectomycorrhizal fungal community is dominated by taxa with certain functional traits (ie, exploration type, melanin concentration and the potential to produce peroxidases).  This work has been published in Ecology. We then conducted a theoretical modeling experiment, incorporating mycorrhizal processes into the Carbon, Organisms, Rhizosphere, and Protection in the Soil Environment (CORPSE) model. We found that ECM fungi suppress decomposition in temperate deciduous and boreal forests with relatively recalcitrant litter inputs, and with ECM fungi that produce oxidases and necromass-degrading enzymes. This work is published in Soil Biology and Biochemistry.  

We are now testing two mechanisms -- litter decomposability and mycorrhizal fungal function -- in field and growth chamber experiments. 

Collaborators: Caitlin Hicks Pries, Rick Lankau and Ben Sulman.

Funding: DOE Terrestrial Ecosystem Science