Dynamic changes in soil fungal communities and functional groups in response to sugarcane/soybean intercropping with reduced nitrogen fertilizer application

A field experiment was conducted with sugarcane monoculture under 100% nitrogen fertilization (500 kg N ha −1 year −1 , N500) and sugarcane/soybean intercropping under 100% (SN500), 80% (SN400), 60% (SN300), and 40% (SN200) nitrogen fertilizers application. Soil fungal abundances in SN500 and SN400 were significantly higher than those in N500 throughout sugarcane growth period and significantly higher than those in SN300 and SN200 at jointing and ripening stages, possibly because of increased carbon and nitrogen substrates. The variations in alpha diversity index in fungal community composition for SN500 and SN400 were more stable across stages than those for other treatments. At tillering stage, sugarcane/soybean intercropping significantly enhanced the relative abundances of Talaromyces and Trichoderma , which help protecting against phytopathogens, and significantly decreased the percentages of potential phytopathogens of Fusarium and Curvularia , compared to monoculture. Additionally, compared with N500, SN500, and SN400 significantly increased the percentages of Trechispora across stages, which favor plant growth, and significantly decreased the percentages of Fusarium at jointing and ripening stages and Curvularia at jointing stage. However, relative to N500, SN300, and SN200 significantly decreased the percentages of Talaromyces at jointing stage, and SN200 significantly raised the percentages of Curvularia at jointing and ripening stages. FUNGuild-based predictions showed that SN500 and SN400 presented the lowest percentages of phytopathogens among treatments and enhanced the percentages of endomycorrhizal fungi compared with N500 across stages. In conclusion, nitrogen application can be reduced to 400 kg N ha −1 year −1 in sugarcane/soybean intercropping, which facilitates soil health improvement by ameliorating fungal community.