Rhizosphere bacterial communities mediate the effect of maize-soybean strip intercropping and nitrogen management on cadmium phytoextraction

Abstract

Concurrently accomplishing the removal of Cd in soil and maintaining sustainable agricultural production is challenging. Intercropping is a viable agricultural practice-based strategy. Based on a long-term field experiment, we investigated the effects of maize-soybean intercropping and nitrogen application on the rhizobacterial properties, crop growth, and Cd translocation. The results showed that the land equivalent ratio and metal removal equivalent ratio were 1.99 and 1.89 under no nitrogen treatment, and 1.83 and 1.45 under conventional nitrogen application. Compared to monoculture, intercropping significantly reduced the maize grain Cd content. Nitrogen management, rather than cultivation mode, was the primary factor determining Cd contents in soybean rhizosphere and roots. These factors also influenced the rhizobacterial communities of maize and soybean. Intercropping significantly increased maize rhizobacterial diversity while decreasing network complexity. Consequently, changes in microbial properties caused maize grain Cd content to decrease following intercropping. Soybean rhizobacterial network module abundances and topological properties were influenced by nitrogen management or cultivation mode, which were closely related to Cd content in the rhizosphere and root. This study demonstrates that intercropping enables maize and soybean to recruit various rhizobacterial communities via specialized strategies, resulting in specific Cd turnover patterns throughout the soil-root-plant continuum that survive from Cd stress. Our findings reveal the unique mechanisms by which rhizobacteria mediate crop-crop intercropping to remove Cd from cropland, emphasizing intercropping's potential to achieve overyielding while remediating heavy metal pollution.