Direct Routes for Microbial Carbon Stabilization of Volatile Organic Compounds in Soil
Juliana Gil-Loaiza1* (firstname.lastname@example.org), Parker Geffre1, Jordan Krechmer2, Malak Tfaily1, Linnea Honeker1, J. Rob Roscioli2, Joanne Shorter2, Elizabeth Lunny2, Manjula Canagaratna2, Megan Claflin2, Joseph Palmo3, David Hagan3, Eben Cross3, Kolby Jardine4, Romy Chakraborty4, Eoin Brodie4, and Laura K. Meredith1
1University of Arizona; 2Aerodyne Research, Inc.; 3QuantAQ, Inc.; and 4Lawrence Berkeley National Laboratory
The overarching project goal is to verify and quantify volatile organic compounds (VOCs) as direct and indirect contributors to soil carbon (C) stabilization within the rhizosphere and beyond through teleconnections, and to determine their underpinning ecological and metabolic mechanisms. The long-term motivation for this project is to transform the current conceptual understanding and predictive capacity of microbial systems and soil C stabilization to include the important roles of volatile compounds. This presentation falls under the objective to determine the direct pathways and contributions of root-released VOCs and VOC transformations by soil microbiomes to soil C cycling and stabilization. Specifically, in this task, researchers will aim to identify VOC-consuming microbes and traits and identify pathway(s) for VOC-C stabilization in soil pools using soil incubations and time-resolved 13C-VOC stable isotope labeling.
VOCs are ubiquitous carbon pools in the Earth system, but often remain uncharacterized as vectors of soil organic C transformations. Roots, litter, aboveground vegetation, and microbial metabolism are all sources of VOCs; however, little is known about how these omnipresent metabolites (Honeker et al. 2021; Meredith and Tfaily 2022) can contribute to C cycling in soils. In this project, researchers aim to verify and quantify the direct contributions of VOCs to soil C pools and determine their underpinning ecological and metabolic mechanisms. Here, researchers present the efforts to identify and quantify VOC uptake rates in soil, identify VOC-consuming microbes and traits, and determine whether the VOC uptake contributes to soil C pools. In a first experiment, the team exposed soil columns to controlled amounts of three VOCs (isoprene, methyl vinyl ketone, ethanol) below the soil surface to mimic root emissions. By monitoring subsurface VOC concentrations using novel in situ diffusive soil probes (Roscioli et al. 2021; Gil-Loaiza et al. 2022) connected to a proton transfer reaction time of flight mass spectrometer, researchers identified different uptake capacities for the three VOCs. Furthermore, the team discovered that microbial communities appeared to dramatically enhance their isoprene uptake rates in response to isoprene exposure, revealing that microbial VOC metabolism can acclimate to resource availability. By tracking shifts in community composition and the isoprene monooxygenase gene copy number in these experiments, the aim is to identify the responsible microbes and the metabolic pathways involved. In a second experiment, by characterizing shifts in soil C concentration and composition (Fourier-transform ion cyclotron resonance mass spectrometry) in response to additions of different VOCs (methanol, acetaldehyde, acetone, isoprene, and monoterpene ɑ-pinene), researchers will test the hypothesis that VOCs can have a direct impact on soil carbon composition. Researchers will use these results to refine plans for subsequent 13C isotope-labeling experiments to track VOC-C into soil C pools and microbial groups. These experiments will provide new understanding of the direct impacts of VOCs on soil C and the importance to the conceptual models of soil C.
Figure 1. Illustration of the overarching project goal to verify and quantify volatile organic compounds (VOCs) as direct and indirect contributors to soil C stabilization within the rhizosphere and beyond through teleconnections, and to determine their underpinning ecological and metabolic mechanisms.
Honeker, L. K., et al. 2021. “The Volatilome: A Vital Piece of the Complete Soil Metabolome.” Frontiers in Environmental Science 23(9).
Meredith, L. K., and M. M. Tfaily 2022. “Capturing the Microbial Volatilome: An Often Overlooked ‘Ome’.” Trends in Microbiology 30(7), 622–31.
Roscioli, J. R., et al. 2021. “Soil Gas Probes for Monitoring Trace Gas Messengers of Microbial ” Scientific Reports 11(1), 8327.
Gil-Loaiza, J., et al. 2022. “Versatile Soil Gas Concentration and Isotope Monitoring: Optimization and Integration of Novel Soil Gas Probes with Online Trace Gas Detection.” Biogeosciences 19(1), 165–85.
This research was supported by the DOE Office of Science, Office of Biological and Environmental Research (BER), grant nos. DE-SC0023189 and the NSF Signals in the Soil program, grant no. 203419. Part of this work was also performed at Lawrence Berkeley National Laboratory supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research under Contract No. DE-AC02-05CH11231.