Ectomycorrhizal fungi and biochar promote soil recalcitrant carbon increases under arsenic stress

Abstract

Globally, vast mining areas (∼31,396.3 km²) hold significant potential for soil carbon sequestration. However, the sequestration capacity of mine soils is closely linked to contamination characteristics and restoration strategies. Arsenic, a highly toxic metalloid prevalent in acid mine soils, affects carbon turnover through its interactions with soil compounds. Nevertheless, the underlying mechanisms remain inadequately understood. This study introduces a phytobial remediation approach combining ectomycorrhizal fungus (Suillus luteus) inoculated into Pinus massoniana and biochar as a soil amendment. Results demonstrated that S. luteus extended apoplastic spaces to absorb arsenic into root cell intervals while encapsulating organic matter into aggregates. Biochar further promoted recalcitrant carbon formation, significantly increasing aggregate-carbon, particulate organic carbon (POC), and mineral-associated organic carbon (MAOC) by 3.15-, 1.74-, and 2.33-fold, respectively, compared to controls. Distinct hyphosphere microbiomes were observed in the combined treatment (BS), with enhanced microbial diversity, enzyme activity, carbon-sequestration genes, and necromass production, indicating the pivotal role of soil microorganisms in stable carbon pool formation. These synergistic effects not only facilitated arsenic detoxification but also significantly contributed to carbon stabilization.