Generalists and specialists decomposing labile and aromatic biochar compounds and sequestering carbon in soil

Biochar plays an important role in soil carbon (C) sequestration, while the effectiveness of sequestration is mostly determined by microbial preferences to utilize the different biochar components (i.e. labile substances or fused aromatic backbone). Thus, it is important to investigate the responses of the bacterial community and specific taxa, and associated C metabolic functions to biochar labile C (i.e. easily mineralizable C) or aromatic backbone (i.e. persistent C). Here, we separated the biochar components into labile C and aromatic backbone, and used the 16S sequencing in conjunction with the addition of an internal standard to quantify the absolute copy number of various bacterial taxa. The aromatic backbone decreased microbial metabolic quotient by 47 %, incorporating more C into biomass and contributing to C sequestration rather than releasing it into the atmosphere, while the labile C caused the opposite trends. The bacterial generalists utilizing aromatic backbone and labile C were mainly from Oxalobacteraceae (Proteobacteria) and Sporosarcina (Firmicutes). The bacterial specialists responsive for aromatic backbone were from Myxococcaceae and Flavisolibacter, while those responsive to labile C were from Ktedonobacteraceae and Bradyrhizobiaceae. Microbial abundance of specialists responsive to labile C was 3.3 times larger than those responsive to aromatic backbone, indicating the preferences of labile C specialists for energy sources and aromatic C specialists for slow utilization of persistent C in versatile habitats. Our work revealed microbial strategies for utilization of organic substances of very contrast availability, and their contributions to soil C sequestration depending on biochar components.