12 May 2021

12 May 2021

Review status: this preprint is currently under review for the journal BG.

Labilization and diversification of pyrogenic dissolved organic matter by microbes

Aleksandar I. Goranov1,a, Andrew S. Wozniak2, Kyle W. Bostick3,b, Andrew R. Zimmerman3, Siddhartha Mitra4, and Patrick G. Hatcher1 Aleksandar I. Goranov et al.
  • 1Department of Chemistry and Biochemistry, Old Dominion University, Norfolk, VA, USA
  • 2School of Marine Science and Policy, College of Earth, Ocean, and Environment, University of Delaware, ewes, DE, USA
  • 3Department of Geological Sciences, University of Florida, Gainesville, FL, USA
  • 4Department of Geological Sciences, East Carolina University, Greenville, NC, USA
  • acurrent address: Department of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, Troy, NY, USA
  • bcurrent address: Fugro GeoServices, 6100 Hillcroft Avenue, Houston, TX, USA

Abstract. With the increased occurrence of forest fires around the world, interest in the chemistry of pyrogenic organic matter (pyOM) and its fate in the environment has increased. Upon leaching from soils by rain events, significant amounts of dissolved pyOM (pyDOM) enter the aquatic environment and interact with microbial communities that are essential for cycling organic matter within the different biogeochemical cycles. To evaluate the bio-reactivity of pyDOM, aqueous extracts of laboratory-produced chars were incubated with soil microbes and the molecular changes to the composition of pyDOM were probed using ultrahigh resolution mass spectrometry (Fourier transform – ion cyclotron resonance – mass spectrometry). Given that photo-degradation also affects the composition and reactivity of pyDOM during terrigenous-to-marine export, the effects of photochemistry were also evaluated in the context of the bio-reactivity of pyDOM.

Ultrahigh resolution mass spectrometry revealed that, after incubation, many different (both aromatic and aliphatic) compounds were degraded, and new labile compounds, 22–40 % of which were peptide-like, were produced. This indicated that a portion of pyDOM has been labilized into microbial biomass during the incubations. Fluorescence excitation-emission matrix spectra revealed that some fraction of these new molecules is associated with fluorophores from proteinaceous and/or autochthonous/microbial biomass origin. Two-dimensional 1H-1H total correlation NMR spectroscopy identified a peptidoglycan-like backbone within the microbially produced compounds. These results are consistent with previous observations of nitrogen from peptidoglycans within the soil and ocean nitrogen cycles.

Interestingly, the exact nature of the bio-produced organic matter was found to vary drastically among samples indicating that the used microbial consortium may produce different exudates based on the composition of the initial pyDOM. Another potential explanation for the vast diversity of molecules is that microbes only consume low molecular weight compounds, but they also produce reactive oxygen species (ROS), which initiate oxidative and recombination reactions that produce new molecules. The observed microbially-mediated diversification of pyDOM suggests that pyDOM contributes to the observed large complexity of natural organic matter. More broadly, pyDOM can be substrate for microbial growth and be incorporated in environmental food webs.

Aleksandar I. Goranov et al.

Status: open (until 23 Jun 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-23', Anonymous Referee #2, 21 May 2021 reply

Aleksandar I. Goranov et al.

Aleksandar I. Goranov et al.


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Short summary
Wildfire-derived molecules are ubiquitous in the aquatic environment, but their biotic fate remains understudied. We have evaluated the compositional changes that occur to wildfire-derived molecules after incubation with soil microbes. We observe a significant degradation, but also a production of numerous new labile molecules. Our results indicate that wildfire-derived molecules can be reworked and consumed by microbes leading to their incorporation into food webs and the global carbon cycle.