Objective   Effects of underground interactions between roots of maize and soybean plants under intercropping on plant photosynthesis, crop yield, and soil physiochemical properties were investigated to decipher the associated mechanisms.

  Method  A maize/soybean intercropping experimentation was conducted in the field. Underground between the maize and soybean plants, a plastic sheet to completely separate and deprive interactions between the root systems (Q), a nylon mesh to partially block the underground interactions (W) or with no artificial barrier to allow total root-interactions (N) was implemented. SPAD, photosynthetic characteristics, and yield of the plants grown under the varied degrees of partition on the root systems were measured.

  Result   Compared to monoculture, the intercropped maize and soybean under N showed increased chlorophyll contents in the functional leaves by 10.36% and 9.65%, respectively. The net photosynthesis, stomatal conductance, intercellular CO₂ concentration, and transpiration rate were also significantly enhanced by the intercropping under varied roots partitions as they ranked N＞W＞Q＞monoculture. The crop yields of the plants were improved by the intercropping under W or N. The land equivalent ratio (LER) of the N treatment was 1.39, while that of W 1.13. Under Q or W, the contents of total and available N, P, and K in rhizosphere soil were higher than those in the monoculture lot. The activities of catalase, acid phosphatase, urease, sucrase, and peroxidase increased in the rhizosphere soil under W or N. A significant correlation was observed between part of the enzyme activity and nutrient content in the soil.

  Conclusion  The interactions between the root systems of the intercropped maize and soybean plants might activate the nutrient pool and enzyme activity in the rhizosphere soil. The leaf chlorophyll of the intercropped plants could also be increased by the underground interactions benefitting the plant photosynthesis with improved crop yield.