Spent mushroom substrate mediates lead-cadmium immobilization and plant growth in tailings: Enhanced phosphorus...

Mining activities cause severe heavy metal dispersion in tailings, threatening regional water and food security. The global mushroom industry generates enormous spent mushroom substrate (SM), a promising organic material for mine restoration. However, mechanistic comparisons between SM and three specific inorganic amendments (calcium carbide slag, CS; phosphogypsum, PG; coal gangue, CG) remain limited. A 60-day pot experiment on heavily polluted lead-zinc tailings (total lead: 16733 mg/kg; total cadmium: 78.04 mg/kg) compared SM with CS, PG, and CG treatments. SM reduced bioavailable cadmium by 50.46 %, lowered mild acido-soluble cadmium from 81.88 % to 70.15 %, and decreased plant cadmium. Higher bioavailable lead under SM still reduced root lead accumulation by 62.31 %. Microbially, SM enriched key functional microbes: Bacteroidetes rose from 2.66 % to 29.67 %, Leucobacter increased by 30.43 %, and AMF spore density increased tenfold. These shifts were associated with metal transformation and immobilization, reducing root cadmium and lead accumulation. Functional predictions indicated potential enhancement of microbial metal detoxification and organic phosphorus mineralization. Despite higher total phosphorus in PG, SM exhibited superior phosphorus availability. Improved nutrient supply and metal immobilization boosted photosynthetic rate by 230.89 % and lowered malondialdehyde (P < 0.0001). CS suppressed microbial diversity, probably through elevated pH, and CG exerted negligible remediation effects. Partial least squares structural equation modeling (PLS-SEM) revealed that soil nutrients indirectly lower metal bioavailability, linking soil fertility to plant performance. This study demonstrates that SM remediates tailings via integrated chemical and biological regulation, providing sustainable waste recycling for mine rehabilitation.