Evergreen camphor and deciduous N2-fixer alder differently impact soil bacterial communities and N and P cycling in a Cupressus funebris monoculture

Abstract Background and Aims Transferring pure forests to more resilient and productive mixtures is commonly recommended. However, how introduced species with different identities impact the soil microbiome and nutrient cycling is not well understood. Methods We investigated the changes of soil physicochemical properties and microbial community following admixing the evergreen deep-rooting camphor ( Cinnamomum camphora ) and the deciduous N 2 -fixer alder ( Alnus cremastogyne ) into a pure cypress ( Cupressus funebris ) forest. Results Admixing significantly enhanced soil water, total nitrogen (N) and total phosphorus (P) contents. Soil pH, available P levels as well as alkaline phosphatase (ALP) activity were significantly increased in the vicinity of alder, while the presence of camphor improved available N and potassium (K) contents. Compared to the cypress monoculture, the two mixtures exhibited higher soil microbial diversity and a greater abundance of the dominant phyla Proteobacteria and Acidobacteria. Which contributed to improved soil nutritional status through enhanced N fixation, inorganic P solubilization and organic matter decomposition. In addition, genes related to methanogenesis, nitrification, denitrification and methane oxidation were markedly decreased in the two mixed stands. Our study showed that introducing alder or camphor improved N cycling without causing higher N loss. Moreover, compared to the evergreen camphor, the deciduous N 2 -fixer alder favored bacterial communities stimulating organic P mineralization, nitrite and nitric oxide reduction. Conclusion Our study reveals the significant effects of admixing on the soil bacterial community and its potential effects on nutrient cycling, highlights the importance of introduced species identities, and provides instructions for designing and managing mixed-species stands.