Quercus variabilis is one of the primary species for plantation regeneration across China’s warm-temperate and subtropical zones. However, its long-term monoculture leads to ecosystem instability. Soil fungi are essential for nutrient cycling and ecosystem functioning, yet their responses to oak-dominated mixed plantations remain insufficiently understood. This study investigated the soil fungal communities among Q. variabilis monoculture (QV), mixed plantations of Q. variabilis and Platycladus orientalis (PO), Q. variabilis and Pinus tabuliformis (PT), and Q. variabilis, P. orientalis and P. tabuliformis (PPQ). The results showed that PO and PPQ plantations contained significantly higher concentrations of SOC, TN, and TP compared to QV monoculture. Ascomycota and Basidiomycota were identified as the dominant fungal phyla across four plantation types, with PO exhibiting the highest relative abundance of Ascomycota (60.85%) and fungal alpha diversity. The soil fungal communities across all plantations were predominantly saprotrophic, followed by mixotrophic modes. The relative abundance of saprotrophic fungi was significantly greater in the mixed plantations, peaking in PO at 44.69%. The soil fungal communities in both PO and PPQ plantations exhibited higher network interaction density. The SOC, TN, TP, water content, zinc, and β-glucosidase activity served as key environmental drivers of fungal community composition. Overall, the mixed plantation of Q. variabilis and P. orientalis most effectively improved soil fertility, enhanced fungal diversity, and increased network complexity, suggesting its potential as a sustainable afforestation strategy for oak-dominated ecosystems in the low hilly regions of western Henan. However, these findings are based on a single sampling period, and long-term monitoring is required to confirm its sustained ecological benefits.

The effects of biochar on soil N₂O emissions remain contentious, and the microbiological processes involved are not yet fully understood. Arbuscular mycorrhizal (AM) fungi, key players in soil nitrogen (N) cycling, may mediate the impact of biochar on plant N uptake and N₂O emissions, but this interaction remains unclear. This study involved a two-year field experiment to examine how varying biochar application rates affect soil microbial communities, particularly AM fungi at rainfed maize (Zea mays L.) farmland, and to assess how AM fungi influence soil N₂O emissions and maize growth under biochar addition with two AM fungi treatments (with and without suppression of native AM fungi). The results revealed that biochar significantly enhanced soil microbial diversity, especially the variety and richness of AM fungi. Biochar addition improved soil physicochemical parameters, including soil water content, bulk density, and inorganic N availability. Biochar also decreased AOA and AOB gene abundances, increased AM fungal gene abundances, lowered (nirK + nirS)/nosZ ratio, and reduced soil N₂O emissions. Suppression of native AM fungi increased N₂O emissions throughout the rainfed maize growing period, accompanied by a higher (nirK + nirS)/nosZ ratio. Biochar addition combined with non-suppressed AM fungi promoted maize growth, with the highest yield observed at 20 t ha⁻¹ biochar. Overall, biochar decreased N₂O emissions and strengthened the performance of AM fungi in rainfed maize farmland, highlighting the vital role of AM fungi s in soil N cycling under biochar addition. This study offers a scientific basis for using biochar in reducing N₂O emissions and increasing crop yield in dry farmland.