Maize/soybean intercropping improves stability of soil aggregates driven by arbuscular mycorrhizal fungi in a black soil of northeast China

It is demonstrated that intercropping improves soil fertility, but its effect on deep soil is still unclear. The major objective of this study was to determine the distribution of arbuscular mycorrhizal fungi (AMF) and soil aggregates and their interrelationship across soil depths in intercropping systems. A three-year positioning experiment based on a two-factor experimental design at two N application levels (N0 and N2) and different cropping systems (maize/soybean intercropping and corresponding monocultures) was started in 2017. Soil samples were collected from 0–15 cm and 15–30 cm for analyzing soil aggregates and from 0–15 cm, 15–30 cm, 30–5 cm, and 45–60 cm for determining the AMF composition. It was observed that intercropping improved the macro-aggregate (> 5 mm) content at 0–15 cm and 15–30 cm depths for maize soil and only 0–15 cm depth for soybean soil without N treatment. The application of N decreased the macro-aggregate content in the intercropping soil at 0–15 cm and 15–30 cm depths. Moreover, intercropping significantly improved the AMF diversity of maize and soybean soils across soil depths, while the application of N reduced the AMF diversity of soil across depths. The structural equation modeling analysis indicated that the intercropping system influenced the stability of soil aggregates and promoted the formation of large aggregates by altering soil nutrients and the diversity of AMF. The results further revealed the reasons behind soil fertility improvement by adopting crop diversification.