Biochar derived from feedstock with high lignin content leads to better soil improvement performance in red soils: from the perspective of soil microbial regulation and carbon stabilization.

Red soil in southern China has a significant potential for carbon sequestration enhancement. Therefore, this study aimed to explore more effective biochar options to enhance the soil microbial environment and investigate their effects on soil carbon cycling. Three types of biochar were prepared and analyzed: maize stover biochar (Maize-BC, low lignin content), cotton stover biochar (Cotton-BC, high lignin content), and sludge biochar (Sludge-BC, no lignin content). The structure of the soil microbial community and carbon dynamics were comprehensively analyzed. The three biochars increased soil inorganic carbon, stable organic carbon, microbial carbon, and dissolved organic carbon by 30.1%-75.5%, 37.6%-44.0%, 88.4%-248.1%, and 4.3%-73.9%, respectively. Maize-BC with lower lignin content exhibited higher abundance and diversity in soil microbial communities compared to other treatments. In contrast, the addition of Cotton-BC with higher lignin content resulted in a shift mainly in the phylum Actinobacteria and Proteobacteria. Overall, the soil changes induced by cotton stover were more favorable for promoting a shift in the microbial community structure toward a lower carbon cycle, enabling microorganisms to better regulate or control the soil carbon cycle. This study offers a promising approach for future research focused on enhancing soil fertility and reducing soil carbon emissions.