Carbon sequestration potential and physicochemical properties differ between wildfire charcoals and slow-pyrolysis biochars
 Swansea Univ, Dept Geog, Coll Sci, Singleton Pk, Swansea SA2 8PP, W Glam, Wales;  Swansea Univ, Dept Biosci, Coll Sci, Singleton Pk, Swansea SA2 8PP, W Glam, Wales; m Univ Santiago de Compostela, Dept Soil Sci & Agr Chem, Lugo 27002, Spain;  Agroscope, Environm Analyt, Reckenholzstr 191, CH-8046 Zurich, Switzerland;  Scottish Univ Environm Res Ctr, NERC RCF, Rankine Ave,Scottish Enterprise Technol Pk, E Kilbride G75 0QF, Lanark, Scotland;  Rice Univ, Dept Earth Environm & Planetary Sci, 6100 Main St MS 126, Houston, TX 77005 USA
Pyrogenic carbon (PyC), produced naturally (wildfire charcoal) and anthropogenically (biochar), is extensively studied due to its importance in several disciplines, including global climate dynamics, agronomy and paleosciences. Charcoal and biochar are commonly used as analogues for each other to infer respective carbon sequestration potentials, production conditions, and environmental roles and fates. The direct comparability of corresponding natural and anthropogenic PyC, however, has never been tested. Here we compared key physicochemical properties (elemental composition, delta C-13 and PAHs signatures, chemical recalcitrance, density and porosity) and carbon sequestration potentials of PyC materials formed from two identical feedstocks (pine forest floor and wood) under wildfire charringand slow-pyrolysis conditions. Wildfire charcoals were formed under higher maximum temperatures and oxygen availabilities, but much shorter heating durations than slow-pyrolysis biochars, resulting in differing physicochemical properties. These differences are particularly relevant regarding their respective roles as carbon sinks, as even the wildfire charcoals formed at the highest temperatures had lower carbon sequestration potentials than most slow-pyrolysis biochars. Our results challenge the common notion that natural charcoal and biochar are well suited as proxies for each other, and suggest that biochar’s environmental residence time may be underestimated when based on natural charcoal as a proxy, and vice versa.
Citation: Santín, C., Doerr, S. H., Merino, A., Bucheli, T. D., Bryant, R., Ascough, P., Masiello, C. A. (2017). Carbon sequestration potential and physicochemical properties differ between wildfire charcoals and slow-pyrolysis biochars. Scientific Reports, 7(1). https://doi.org/10.1038/s41598-017-10455-2