Higher Growth Promotion of Maize (Zea mays L.) than Soybean [Glycine max (L.) Merrill] by Mycorrhiza Helper Kitasatospora in an Intercropping System

As natural bioenhancers of arbuscular mycorrhizal (AM) symbiosis, mycorrhiza helper (MH) bacteria have been proposed to develop sustainable agriculture. However, the inoculation effects of MH bacteria in intercropping systems remain poorly understood. Here, a greenhouse pot experiment was conducted to reveal the performance and role of an indigenous AM fungal community in a black soil under maize–soybean intercropping in response to the inoculation of two MH strains, Kitasatospora herbaricolor 2023A-1 (KHe) and K. indigofera 2023A-2 (KIn). Both strains shifted the most dominant AM fungal genus from Paraglomus to Glomus and promoted the occurrence of previously undetected genera Diversispora and/or Gigaspora. Nevertheless, only KIn significantly increased AM fungal diversity indices, whereas both strains increased AM fungal abundance and soil available P supply capability. Within the intercrops, maize exhibited higher mycorrhizal colonization and stronger responses in shoot biomass and P and K acquisition than the neighboring soybean. Moreover, compared with any single strain, the KHe + KIn produced greater increases in soil actinomycetes population, AM fungal abundance and colonization, soil alkaline phosphatase activity and available P concentration, nutrient acquisition and plant growth, particularly with maize. These findings provide new insights into the potential usage of MH bacteria in intercropping systems in black soils.