Review on the effects of biochar amendment on soil microorganisms and enzyme activity

Purpose The multiple benefits of biochar use as a soil amendment has garnered global attention. Biochar addition is a crucial factor to improve soil biomass, soil enzyme activities, microbial biomass and improve soil nutrient utilization rate. However, the precise mechanism of effects of biochar addition on microbial community structure and diversity, as well as enzyme activity, remains unclear, especially for biochar obtained from different pyrolysis temperatures and variable quantities in which it is applied to soil. Materials and methods We compiled and summarized the existing literature on the impacts of biochar on microorganisms and enzymes, with a specific on articles published over a five-year period (2018–2022). This review provides a comprehensive review of the relevant literature on enzyme activity, microbial diversity, community structure and abundance following biochar amendment in soil, and further elucidates the underlying mechanisms of biochar-induced effects on various factors. Results and discussion The impact of biochar on soil microorganisms could be categorized into three aspects: (1) biochar, due to its porous structure and high surface area, functions as a sanctuary for soil microorganisms; (2) biochar provides essential elements such as carbon (C) and nitrogen (N) sources to soil microorganisms, and finally (3) biochar improves the survival conditions of soil microorganisms by modifying soil pH, CEC, aggregation, and enzyme activity. Importantly, biochar produced at lower pyrolysis temperatures provides valuable C and N for soil microorganisms. Whereas biochar obtained at higher pyrolysis temperatures contains much less active C and N. However, it still contributes to microbial nutrition through diverse mechanisms, e.g., nutrient immobilization and increased nutrients residence time through its bonding with soil labile C. Conclusions This review found that the type of source material and pyrolysis temperature were the primary determinants in the impacts of biochar on soil microbial abundance, community structure, and diversity.