Long-term peanut shell biochar application improves soil fertility and bacterial network stability across tobacco-growing regions in China

Abstract Soil microorganisms are central to nutrient cycling and soil fertility, and their dynamics are strongly influenced by agricultural management practices. Peanut shell biochar has been widely applied to enhance soil fertility and reduce nutrient loss. However, its long-term effects on soil microbial communities under large-scale field conditions remain poorly understood. To address this knowledge gap, we conducted multi-year field experiments across five major tobacco-growing regions in China. Compared with the control group, long-term addition of peanut shell biochar significantly improved various soil chemical properties in Mudanjiang, Shangluo, Yichun, and Yanshan Town, including pH, available potassium, available phosphorus, organic matter, carbon-to-nitrogen ratio, alkaline hydrolyzable nitrogen, sucrase activity, catalase activity, and urease activity, while reducing the available phosphorus and catalase activity in Xuchang. Soil microbial diversity and community composition exhibited significant variation across sites, primarily shaped by differences in soil chemical properties. Although overall microbial diversity was not significantly altered by biochar addition, specific taxa, such as Firmicutes, Zoopagomycota, and Blastocladiomycota, were enriched, with Bacilli representing 70% of the significantly enriched bacterial taxa. Co-occurrence network analysis revealed that biochar amendment enhanced the complexity and stability of bacterial networks but reduced those of fungal networks. Furthermore, long-term biochar application enhanced soluble sugar content through pathways involving soil organic matter, bacterial community diversity, and specific enriched bacterial taxa. Collectively, these findings underscore the important role of peanut shell biochar in promoting the stability of bacterial networks and enhancing crop quality, providing a sustainable strategy for improving soil health and agricultural productivity. Graphical Abstract