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This research explored the effects of the addition of low doses of aromatic plant biomasses (APBs) on the microbial community and carbon source decomposition in compost. APBs were reported to be capable of altering the composition and function of microbial communities in many environments. However, the effects of APB addition on the compost carbon source metabolism, a process highly linked to the microbial community of compost, were still unclarified, especially when added in small doses. In this study, Cinnamomum camphora biomass was added to the initial compost of Stropharia rugosoannulata cultivation materials, in a mass ratio of 0%, 1%, 2%, and 3%, respectively. The variation in the carbon source contents, the microbial community composition, and the related enzyme activities of the end compost products were measured. The results showed that Cinnamomum camphora biomass addition significantly altered the content of cellulose, hemicellulose, lignin, and protein of compost products, but did not affect the starch and soluble sugar content. Meanwhile, the addition significantly reduced lignin peroxidase and cellulase activities, but increased xylanase and laccase activities, and had no effect on magnesium peroxidase and polyphenol oxidase. Both the bacterial and fungal community compositions were significantly altered by the addition, though the alpha diversity indexes were not significantly changed. The relative abundance of Proteobacteria and Sordariomycetes was significantly increased by the addition, while Acidobacteria, Chloroflexi and Eurotiomycetes significantly decreased. Structural equation modeling found that the variation in the bacterial community composition (0.464 standard total effect) provided a higher contribution to lignocellulose degradation, rather than the fungal community (0.365 standard total effect). A co-occurrence network analysis further revealed that the trade-off between lignin peroxidase and laccase activity, which was induced by the relative abundance variation in Proteobacteria, Actinobacteriota, and Firmicute members, was the main driver in the lignocellulose decomposition variation. This research provides a new insight into the recycling of APB waste, and offers an improvement to mushroom cultivation material compost.