Stabilizing Active Aluminum (Al3+) in Acidic Soils via Biochar-Induced Microbial Niches: Focusing on Denitrifier-Mediated Mechanisms, Efficiency, and Environmental Outcomes

The pervasive toxicity of active aluminum (Al3+) in acidic red soils threatens agroecosystem sustainability, with conventional chemical stabilizers facing cost and secondary pollution constraints. This study evaluated rice husk/sawdust and their pyrolysis-derived biochar as stabilizers, focusing on microbial synergy. Results showed 3% rice husk biochar (RB) achieved 22.1 ± 1.1% stabilization efficiency within 180 days, outperforming sawdust biochar (12.1 ± 0.8%) and raw biomass. Biochar’s alkalinity and porosity created neutral niches, enriching denitrifiers (Thiobacillus, Arthrobacter, Thermomonas) that elevated pH, promoted Al(OH)3 precipitation, and enhanced oxygen-containing functional groups. This work valorizes agricultural waste for long-term Al3+ toxicity mitigation.