Effects of compound fertilizer decrement combined with silkworm excrement organic fertilizer on soil enzyme activities and microbial nutrient limitation in <i>Phyllostachys edulis</i> forests.

The combination of compound fertilizer and organic fertilizer is an effective means to improve soil fertility and promote plant growth. To clarify how compound fertilizer (CF) decrement and silkworm excrement organic fertilizer (OF) application affects soil enzyme activity and microbial nutrient limitation in moso bamboo (<i>Phyllostachys edulis</i>) forests, we set up an experiment with six treatments: five substitution ratios of 0, 25%, 50%, 75%, and 100% (CF, OF₂₅, OF₅₀, OF₇₅, OF) and no fertilization (CK). We investigated the changes in soil basic chemical properties, microbial biomass, enzyme activities, and enzyme stoichiometric ratios, and evaluated the main factors affecting enzyme activity and enzyme stoichiometric ratios. The results showed that compared with CK and CF, OF₅₀, OF₇₅, and OF significantly increased soil organic carbon (SOC), total nitrogen (TN), total phosphorus, and available phosphorus content by 30.3%-80.5%, 30.9%-84.6%, 11.5%-143.9%, and 3.5%-487.0%, respectively, and significantly increased the activities of soil β-1,4-glucosidase, β-1,4-N-acetylglucosamine glucosidase, leucine aminopeptidase, and acid phosphatase. Compared with CF, soil microbial biomass carbon in OF₅₀, OF₇₅, and OF was significantly increased by 17.0% to 27.1%, and soil microbial biomass nitrogen in OF₅₀ was significantly increased by 38.7%. Compared with CF, OF significantly decreased the stoichiometric ratio of C- and N- acquiring enzymes (C:N_EEA) and increased that of N- and P-acquiring enzymes (N:P_EEA), while OF₇₅ significantly increased that of C- and P-acquiring enzymes (C:P_EEA). The enzyme quantification vector model indicated that soil microorganisms were mainly limited by nitrogen. OF₇₅ and OF significantly weakened the nitrogen limitation of microorganisms. Relevant analysis and redundancy analysis revealed that SOC, TN, alkali-hydrolyzable nitrogen, and cation exchange capacity were significantly positively correlated with enzyme activities and enzyme stoichiometric ratios, which mainly explained the variations of enzyme activities and enzyme stoichiometric ratios. In conclusion, CF decrement combined with OF could significantly increase soil organic carbon, nutrient contents, and enzyme activities, thereby change the nutrient limitation of soil microorganisms. 75% decrement CF combined with OF could alleviate the nitrogen limitation of soil microorganisms and improve soil fertility.