Effects of physical, chemical, and biological ageing on the mineralization of pine wood biochar by a Streptomyces isolate

Abstract

If biochar is to be used for carbon (C) management, we must understand how ageing affects biochar C mineralization. Here, we incubated aged and unaged eastern white pine wood biochar produced at 350 and 550 °C with a Streptomyces isolate, a putative biochar-decomposing microbe. Ageing was simulated via exposure to (a) alternating freeze-thaw and wet-dry cycles (physical ageing), (b) concentrated hydrogen peroxide (chemical ageing) and (c) nutrients and microorganisms (biological ageing). Elemental composition and surface chemistry (Fourier Transform Infrared spectroscopy) of biochar samples were compared before and after ageing. Ageing significantly increased biochar C mineralization in the case of physically aged 350 °C biochar (p < 0.001). Among 350 °C biochars, biochar C mineralization was positively correlated with an increase in O/C ratio (R² = 0.78) and O-containing functional groups (R² = 0.73) post-ageing, suggesting that surface oxidation during ageing enhanced biochar degradation by the isolate. However, in the case of 550 °C biochar, ageing did not result in a significant change in biochar C mineralization (p > 0.05), likely due to lower surface oxidation and high condensed aromatic C content. These results have implications for the use of biochar for long term C storage in soils.