Mixing with broad-leaved trees shapes the rhizosphere soil fungal communities of coniferous tree species in subtropical forests

Abstract Although replanting broad-leaved trees in coniferous forest has been proven to increase stand soil quality, it is unclear how this prevalent forest management regime affects the soil fungal communities of individual conifers in mixed forest. Herein, we chose two representative coniferous tree species (Pinus massoniana and Pinus elliottii) and employed high-throughput sequencing and quantitative PCR to investigate fungal community composition and function in rhizosphere soils under monoculture and in mixed forests (replanted with Schima superba for 13 years) in subtropical China. Mixing with broad-leaved trees resulted in increased rhizosphere soil organic carbon (SOC) and nutrient (total nitrogen, NH4+ and available phosphorus). Rhizosphere soil fungal abundance (ITS gene copy numbers) and community diversity of conifers were increased after mixing. Meanwhile, the soil fungal abundance and ACE richness index in Masson pine were higher compared with slash pine whether in monoculture or mixed forests. Ascomycota, Basidiomycota, Mortierellomycota and Glomeromycota were the dominant phyla in soils. Mixing with broad-leaved trees decreased the relative abundance of Ascomycota, while it increased Basidiomycota and Glomeromycota in the rhizosphere soil of conifers. Moreover, there was a decrease in the relative abundance of animal pathogens and wood saprotrophic fungi, while soil saprotrophic fungi, ectomycorrhizal and arbuscular mycorrhizal fungi were increased in rhizosphere soil of conifers after mixing, suggesting changes from saprotrophic fungi to symbiotrophic fungi to increase soil nutrient supply and enhance tree nutrient uptake. Principal coordinates analysis showed that the fungal communities in mixed forests clustered closely and were separated from monoculture forests. Fungal community composition and function were mainly dependent on SOC. Our results indicate that mixing with broad-leaved trees increases fungal abundance, alters fungal community composition and function and thus potentially contributes to soil quality improvement and tree nutrient acquisition of conifers. Masson pine is more adaptable than slash pine to establish mixed forest in subtropical China.