Potential bioavailability of pyrogenic organic matter resembles natural dissolved organic matter pools

Abstract

Wildfires are increasing in severity and extent, creating many negative consequences for aquatic ecosystems. Pyrogenic materials generated by wildfires are transported across terrestrial landscapes into inland waters, where ~10% of organic matter pools may be comprised of black carbon (BC), a major component of pyrogenic organic matter (PyOM). Yet, the heterogeneity of PyOM from various fuels and burn conditions complicates efforts to understand its bioavailability. We used a substrate-explicit model to predict the energy content, metabolic efficiency, and rate of aerobic decomposition of representative PyOM compounds. This enabled us to systematically evaluate a full spectrum of PyOM chemistries that is unfeasible with laboratory experiments. The model relies on the elemental stoichiometry, allowing comparison of known PyOM chemistry to formula assignments of natural organic matter (NOM) from a recent high resolution mass spectrometry assessment of global aquatic NOM. Overall, we found the range of predicted bioavailability of PyOM was similar to NOM. Phenolic and BC molecules had lower metabolic efficiency than other PyOM and NOM compounds, and BC metabolism was less negatively impacted by oxygen limitation. In total, our work supports the recent paradigm shift regarding PyOM bioavailability, highlighting its potential role in global C emissions as the prevalence of wildfires increases.

Playing with FiRE: A genome resolved view of the soil microbiome responses to high severity forest wildfire

“…Lastly, we show that wildfire and the post-fire soil chemical environment results in a microbiome that actively degrades aromatic compounds likely formed during fire (Figure 5). This finding supports recent studies suggesting that pyrogenic organic carbon is more labile than previously thought 106 , with implications for the modeling of C storage in wildfire impacted ecosystems. Further work is needed integrating multi-omics data from both field observations and laboratory experiments into ecosystem models to refine the quantification of C fluxes in post-fire ecosystems.…”

Molecular insights and impacts of wildfire-induced soil chemical changes

“…Thermodynamic calculations and laboratory experiments [122][123][124][125][126][127] suggest that PyOM is less resistant (that is, more susceptible) to microbial degradation than previously thought. A 2008 analysis of PyOM with solid-state nuclear magnetic resonance spectroscopy, near-edge X-ray absorption fine structure spectroscopy, and X-ray photoelectron spectroscopy of Brazilian soils suggested that PyOM remains stable in soils for centuries to millennia 128 .…”

“…A 2008 analysis of PyOM with solid-state nuclear magnetic resonance spectroscopy, near-edge X-ray absorption fine structure spectroscopy, and X-ray photoelectron spectroscopy of Brazilian soils suggested that PyOM remains stable in soils for centuries to millennia 128 . However, thermodynamic calculations using representative PyOM and unburned dissolved organic matter (DOM) compounds published in 2023 demonstrate substantial overlap between the predicted metabolic rates of PyOM and DOM microbial degradation 127 . Thus, PyOM might not be as markedly resistant to microbial degradation as previously presumed, especially when compared with unburned DOM.…”