Biochar application decreases heavy metal accumulation in ants (Formica japonica)

Biochar enhances soil fauna resilience, yet the underlying molecular mechanisms remain unclear. Here, we investigated heavy metal accumulation by ants (Formica japonica) integrating physiological, biochemical, and transcriptomic analyses. The ants were exposed to both simulated heavy metal mixtures (HM) and real-world mine soil (HZ). Biochar amendment significantly increased ant survival rates (from 70% to 85% in HM) and mitigated weight loss. This physiological improvement stemmed from a dual mechanism: the abiotic immobilization of toxic metals (reducing Cr by 67% in HM and Pb by 76% in HZ) via biochar's physicochemical properties, and the biotic regulation of essential zinc via the upregulation of ZIP transporters. Consequently, the concentration of the stress-biomarker metallothionein (MT) significantly decreased. Transcriptomic analysis further revealed that in the HM environment, biochar alleviated the suppression of protein synthesis pathways, thereby restoring cellular homeostasis, facilitating the resumption of constitutive protein synthesis pathways. In the HZ environment, the reduction in contaminant bioavailability mediated by biochar facilitated metabolic regulation and energy conservation, thereby obviating the need for high-cost emergency responses. These findings reveal that biochar acts as an effective modulator of biological resilience, offering a mechanism-based foundation for ecological restoration.