Abstract: We conducted a field experiment to investigate the effects of biochar derived from three feedstocks (pig manure, peanut shell, and maize straw) on the nutrient limitation status of soil microbial communities and the abundance of functional genes involved in organic carbon degradation in a Phyllostachys edulis forest. Each biochar was applied at a rate of 20 t·hm^-2, with soil without biochar amendment as control. We measured soil and microbial properties after two years. The results showed that all biochar types significantly increased soil pH, soil organic carbon, total phosphorus, and available phosphorus contents. Pig manure biochar significantly reduced soil C:P and alleviated the stoichiometric imbalance between microbial biomass and soil resources. All biochar treatments significantly increased β-glucosidase activity (by 46.5%-131.1%) but decreased the activities of β-N-acetylglucosaminidase (by 20.6%-51.1%) and acid phosphatase (by 23.1%-56.4%). Biochar application significantly intensified microbial carbon limitation while reduced phosphorus limitation and decreased microbial carbon use efficiency, with the most pronounced reduction being observed under pig manure biochar. Biochar application significantly increased the abundances of functional genes of starch, hemicellulose, cellulose, pectin and lignin degradation, following the order of pig manure biochar > peanut shell biochar > maize straw biochar. Random forest analysis indicated that soil total phosphorus and available phosphorus contents were the key factors influencing microbial carbon limitation. Partial least squares path modeling (PLS-PM) indicated that biochar inputs increased microbial carbon limitation by elevating soil pH and alleviating the C:P imbalance, which in turn reduced carbon use efficiency. The degree of microbial carbon limitation exhibited a significant positive effect on the abundance of micro-bial carbon degradation functional genes. In conclusion, biochar from different feedstocks could regulate microbial nutrient limitation by altering soil pH and nutrient stoichiometric balance, thereby affecting microbial carbon metabolic efficiency.

Key words: biochar, soil enzyme activity, stoichiometric balance, carbon-degrading functional gene