Carbon sequestration potential of biochar in soil from the perspective of organic carbon structural modification

Application of biochar derived from biomass resources in soil is an encouraging method to decelerate global warming via carbon sequestration. While there has been extensive research on the priming effect of biochar on the mineralization of native soil organic carbon (nSOC), its correlation with soil organic carbon (SOC) structural variations remains poorly understood. A series of incubation experiments with soils amended with biochar prepared at 300 °C, 450 °C, and 600 °C were performed to explore the shifts in nSOC structure and reveal the interconnections among soil properties, SOC structural variation, and the priming effect induced by biochar. Biochar exhibited an "inhibitory concentration" on soil microorganisms, where 1 % biochar enhanced bacterial and fungal richness and diversity, while 3 % biochar reduced bacterial richness and diversity although soil nutrient conditions were improved. Biochar-treated soil had higher humic acid- and humin-like fractions (HAL and HML) but lower fulvic acid-like components (FAL). Moreover, bulk SOC, FAL, HAL, and HML of soils with 300 °C and 450 °C biochar contained more aromatic-type species (e.g., lignin). Such changes were related to improvement of the soil nutrient condition and shifts in microbial community structures, in addition to the "accumulation of biochar-derived OC in the nSOC pool". Stable carbon isotopes indicated that the inhibitory effect on SOC mineralization (−94.5 to −8.0 mg CO2-C kg−1 soil) induced by biochar was significantly explained by the change in FAL and HAL contents. The findings improved the understanding of the carbon sequestration potential of biochar in soils for SOC structural modification.