Collaborative Research: Exploring the dynamic interaction between pyrogenic carbon and extracellular enzymes and its impacts on organic matter cycling in fire-impacted environments

Fires, whether occurring naturally or caused by human activities, are a pervasive disturbance to many ecosystems and the global carbon (C) cycle. Fires convert tremendous amounts of biomass into CO2 and pyrogenic carbon (PyC) that accumulates in soils. Because of its abundance and unique physicochemical properties, PyC may participate in many soil biogeochemical processes that control the cycling of important elements and soil health.

However, it remains poorly understood how PyC is decomposed in soil and how PyC may affect the soil microbial community – the main driver of soil organic matter (SOM) decomposition. Because microbial decomposition of SOM is catalyzed by enzymes released by microbes (exoenzymes), this project will study how PyC interacts with exoenzymes, and which enzymes are capable of degrading PyC.

Results from this work will fundamentally advance the current understanding of the cycling of PyC and its contribution to the global C cycle. Two graduate students and several undergraduate students from the collaborating institutions will gain interdisciplinary training in biogeochemistry, enzymology, and analytical chemistry. In collaboration with local schools and museums, the team will develop K-12 and community outreach activities to increase general public’s awareness of the role of fires in climate and soil science.

The overarching goal of this proposed project is to explore the roles of PyC in microbial-mediated SOM degradation, particularly its direct impacts on exoenzyme functioning in soils. The role of PyC as an adsorptive surface in soil will first be evaluated, considering its overall large specific surface area and adsorption capacity. Mechanisms of interaction between representative exoenzymes and PyC generated under different combustion conditions and of different weathering histories will be explored, and key properties of PyC and enzymes controlling the interaction will be identified.

Then the impacts of PyC adsorption on enzyme activity will be determined using sensitive calorimetric analyses. Although microbes are known to be capable of degrading and utilizing PyC as a carbon source, the degradation process and effects of abiotic weathering are not clear. Therefore, the rate and structural transformation of PyC degradation by enzymes, particularly those that degrade aromatic structures, will be determined.

This work will apply a holistic approach to detail the chemistry of solid and dissolved PyC, using a suite of spectroscopic techniques. By delineating the interfacial behaviors and functionality of exoenzymes and the interplay between abiotic and biotic weathering processes in controlling PyC stability, knowledge generated from this work will fundamentally advance our understanding of SOM cycling in fire-impacted environments.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.