Effects and mechanisms of sustained-release embedded composite biochar in carbon enhancement and acid reduction of acidified black soil

Black soils in Northeast China are undergoing acidification and organic matter degradation, and are in urgent need of efficient and environmentally sustainable improvement technologies. In this study, a novel sustained-release embedded composite biochar material was fabricated through a ball-milling integration process, in which biochar, reduced iron powder, and polymer materials were combined. A systematic screening process was established through the optimization of biochar substrate preparation conditions, the selection of functional loading components, and the development of a sustained-release carrier process. Through physicochemical characterization and evaluation of environmental effects, Chitosan-Fe-Biochar(CS-Fe-BC) and Polyacrylamide-Fe-Biochar(PAM-Fe-BC) were ultimately identified as the optimal materials. A 180-day incubation experiment was conducted under simulated climate conditions representative of Northeast China. Within 180 days, the application of 5‰ CS-Fe-BC[5] increased soil pH by approximately 0.5 units and enhanced SOC content by about 26.88%.The application of different material treatments effectively improved the structural integrity of the soil carbon pool, leading to significant increases in POC, ROC, andMOC contents. The metagenomic sequencing results revealed that, while maintaining overall abundance stability, the composite material reshaped the soil microbial community structure, facilitated the enrichment of functional bacteria involved in carbon fixation and acid mitigation, and achieved carbon enhancement and acid reduction through differentiated metabolic pathways. These findings suggest that the material plays a pivotal role in driving the processes of carbon accumulation and acid mitigation.The research findings may offer novel materialand theoretical support for the sustainable management of black soil acidification in Northeast China.