Sequestration of Soil Organic and Inorganic Carbon by Dual-Enzymatically Induced Carbonate Precipitation

Urease-induced carbonate precipitation in calcareous soil holds great potential for soil inorganic carbon (SIC) formation and soil organic carbon (SOC) sequestration. However, this process is limited by the slow hydration of carbon dioxide, which can be accelerated by carbonic anhydrase (CA). In this study, we present a novel approach where dual-enzyme (urease and CA) induced carbonate precipitation promotes the synergetic sequestration of SIC and SOC. We selected humic substance, such as humic acid (HA), as a natural SOC to investigate its role in regulating SIC formation and its fate in the dual-enzyme system. Our results demonstrate that the dual-enzyme synergistically enhances SIC sequestration by accelerating calcium carbonate precipitation. HA further enhances this effect by binding to urease and CA, altering their secondary structures. Notably, HA is sequestered by the calcium carbonate precipitates via its -COO^- and phenolic -OH. Additionally, while the dual-enzyme promotes soil aggregation, HA further enhances this process by promoting amorphous calcium carbonate formation, inhibiting its crystallization, and reducing calcite crystallinity. This study demonstrates the potential of dual-enzymically synergetic SIC and SOC sequestration and soil aggregate formation, offering a sustainable solution for mitigating global climate change and improving soil stability.