Effects of long-term application of traditional compost and bio-compost on soil microbial community structure and life-history strategies

Introduction Long-term compost application is an important strategy for improving soil fertility and regulating soil microbial communities, but the comparative effects of traditional compost and bio-compost on microbial life-history strategies remain unclear, which is a valuable framework for linking community shifts to soil carbon and nutrient cycling. Methods In this study, a long-term (30-year) field experiment established in 1993 under a winter wheat–summer maize cropping system was used to evaluate the effects of high-rate bio-compost, high-rate traditional compost, low-rate bio-compost, low-rate traditional compost, and an unfertilized control on soil properties, enzyme activities, microbial community structure, and oligotrophic/copiotrophic groups. Results Compost application significantly increased soil organic carbon, total nitrogen, total phosphorus, and soil moisture, with soil organic carbon content in the high-rate bio-compost treatment being 33.8% higher than that of the control. Soil oxidative enzyme activities, including catalase, lignin peroxidase, manganese peroxidase, and laccase, were also enhanced by compost addition. Bacterial diversity was highest under low-rate bio-compost, whereas fungal diversity and trophic strategies showed stronger responses to fertilization. Principal coordinate analysis and permutational multivariate analysis of variance indicated that both bacterial and fungal community compositions were significantly altered by 30 years of compost application. The bacterial oligotroph/copiotroph ratio remained relatively stable among treatments, while the fungal oligotroph/copiotroph ratio decreased significantly under low-rate bio-compost. Specifically, this treatment significantly decreased the relative abundance of the oligotrophic fungal phylum Basidiomycota while increasing the copiotrophic phylum Ascomycota, indicating a shift toward copiotrophic fungal groups. Co-occurrence network analysis showed that the high-rate bio-compost significantly enhanced microbial network complexity, increasing the number of nodes from 419 (control) to 753 and edges from 828 to 1841 in the bacterial network, suggesting enhanced microbial connectivity under high-rate bio-compost application. Correlation, Mantel, and redundancy analyses further identified soil total phosphorus and oxidative enzyme activities, especially manganese peroxidase, lignin peroxidase, and laccase, as key factors associated with microbial community variation and trophic group distribution. Conclusion Overall, long-term bio-compost application improved soil fertility, stimulated oxidative enzyme activities, enhanced microbial network complexity, and regulated microbial life-history strategies, with different responses between bacterial and fungal communities.