Biochar induces mineralization of soil recalcitrant components by activation of biochar responsive bacteria groups

Amendment of soil with biochar induces a shift in microbial community structure and promotes faster mineralization of soil organic carbon (SOC), thus offsetting C sequestration effects. Whether biochar induces losses of labile or persistent SOC pools remains largely unknown, and the responsible decomposers await identification. Towards addressing these ends, a C3 soil was amended with Biochar₅₀₀ or Biochar₆₀₀ (pyrolyzed at 500 °C and 600 °C, respectively) produced from a C4-maize feedstock and incubated for 28 days. Combination of stable isotope ¹³C techniques, high-throughput sequencing and Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) allowed changes in soil chemodiversity and biodiversity, as well as their interactive effects on biochar induced SOC mineralization to be elucidated. Results indicated that: i) biochar addition shifted the bacterial community towards dominance of Gemmatimonadetes, Bacteroidia, Alphaproteobacteria and Gammaproteobacteria classes, and coincidence with recalcitrant C components and neutral pH soil; ii) the persistent DOM components (such as condensed aromatics and tannin) were depleted in biochar amended soils, while labile DOM components (such as unsaturated hydrocarbons, lipids, carbohydrates and proteins/amino sugar) were relatively enriched, and; iii) Biochar₆₀₀ promoted additional soil derived CO₂ carbon loss over 28 days (93 mg C kg⁻¹ soil). Collectively, these results suggested that the majority of soil derived CO₂ efflux in biochar amended soils originated from recalcitrant components that were mineralized by the persistent organic matter decomposers. This research highlights the significance of biochar responsive taxa in changes of DOM chemodiversity and potential loss of SOC via mineralization.