Microbial controls on biogeochemical cycling of carbon using stable isotope labeling and other novel techniques

Department of Hydrology and Atmospheric Sciences
Weekly Colloquium

Thursday, December 5, 2019
4:00 pm in Harshbarger 206 ~ Refreshments at 3:45 pm hosted by HASSA

Malak Tfaily
Assistant Professor, UA Department of Environmental Science


Predicted increases in temperatures in Northern peatlands are expected to drive substantial alterations to global carbon (C) cycling. In many peatlands, increased temperatures will drive the decomposition of ancient recalcitrant C pools, as well as a surge of new potentially labile C fluxes, as highly productive plant communities (e.g., sedges) take over these systems. The result will be a large increase in microbial decomposition of ancient C and emissions of the greenhouse gases CO2 and CH4. Much attention and study has focused on the fate of old C, which may decompose as temperatures increase, but the fate of new C inputs resulting from increased plant production remains poorly understood. This “new C” cycle has potential to drive substantial climate forces. Particularly, if hydrologic changes increase anaerobic decomposition of new C (e.g., by priming effect), this then could drive larger contributions to gas emissions, and hence feedbacks related to climate change. Here we examined the priming effect, drivers, and dynamics of the “new C” that is stimulated by climate change in Northern peatlands soil using a stable isotope labeling approach in a long term incubation experiment using surface and deep soil samples. We traced the fate of 13C-glucose added to decomposition incubation into (1) different organic matter (through high-resolution 21T FT-ICR-MS and NMR), then into (2) microbial community (16S rRNA), and finally into (3) greenhouse gases (CO2 and CH4 gas emissions. Glucose addition shifted microbial communities and metabolic pathways deep in the peat core (ancient C) whereas surface soils appeared to be less affected by such perturbation. Deep ancient C pools in the peat core can become sources of carbon dioxide to the atmosphere if the processes contributing to their protection from decomposition are disrupted. Shifts in vegetation accompanied by increase in plant rooting depths can expose deep peat microbial communities to resources favorable for decomposition. This research will help shed new light on the mechanistic basis of biological processes and how these processes change in response to community interactions and shifting environmental condition.


Malak Tfaily, Assistant Professor in the Department of Environmental Science, is an ecosystem scientist with a Ph.D. degree in analytical chemistry from Florida State University. Her research aims to improve the understanding of carbon cycling in terrestrial and aquatic systems, the microbial-organic matter interactions that underlie it, and the controls upon it in dynamically changing systems. She uses a combination of modern and unique analytical molecular, geochemical and isotopic techniques to answer how, where and when organic matter formation and degradation takes place in different ecosystems. Malak’s doctoral research training focused on dissolved organic matter characterization, and her post-doctoral research focused on soil organic matter characterization. Recently her research has advanced to the systems-level integration of detailed organic matter characterization with insights from molecular microbial ecology and plant biology, with the direct goal of distilling the findings of these syntheses for improved predictive modeling of ecosystem and global change. At the University of Arizona, she teaches courses in soil chemistry, environmental and analytical chemistry, carbon cycling, and ecosystem science.