Phosphorus solubilizing bacteria rather than arbuscular mycorrhizal fungi drive maize/faba bean intercropping advantages

Cereal/legume intercropping can enhance phosphorus (P) uptake compared with monocultures. However, the mechanisms through which arbuscular mycorrhizal fungi (AMF) and phosphate solubilizing bacteria (PSB) contribute to the advantages in biomass and P uptake by cereal/legume intercropping remain elusive.

We first analyzed P cycling-related soil microbiome and the associated genes in a long-term low P (LP) and high P (HP) input field experiment. Then we conducted two mesocosm experiments by establishing with two root compartments with the planting patterns of maize monoculture and maize/faba bean intercropping. One compartment of monocultured maize and intercropped faba bean was inoculated with AMF (donor), and the suspensions of LP or HP soils or water was added to the other compartment (receiver) in experiment I to test the legacy effect of soil microbiome conditioned by different field P fertilization, and the following experiment was to detect the effect of specific organic or inorganic PSB on intercropping interactions and advantages.

The abundance and structure of total P cycling-related microbes and genes were comparable between LP and HP soils. The addition of bacterial suspensions significantly enhanced shoot biomass but not P content of receiver maize regardless of the AMF presence or not. With AMF, single inorganic PSB and the mixed inorganic and organic PSB increased the shoot biomass and P content of receiver maize than single organic PSB regardless of monocultured or intercropped receiver maize. However, only the mixed inorganic and organic PSB established intercropping advantages in shoot biomass and P content of receiver maize.

The hyphae from faba bean stimulate the cooperation between organic and inorganic PSB to improve the growth and P content of maize in maize/faba bean mixture. Our study emphasized that maintaining the diversity of AMF and PSB communities in soil is important for the overyielding and P uptake by intercropping.