Rhizosphere microbial communities explain positive effects of diverse crop rotations on maize and soybean performance

In agricultural systems, crop rotation diversity influences soil microbial communities and often increases crop productivity. Yet the specific contributions of microorganisms to crop rotation benefits are unknown. We studied corn (Zea mays L.) and soybean (Glycine max L.) within a two-year corn-soybean rotation and four, four-year, four-crop rotations with varying crop sequences. We hypothesized that rhizosphere microbial communities would predict crop productivity contingent on rotation diversity and previous crop legacy. Sampling at seedling and flowering stages, we assessed rhizosphere bacterial and fungal communities, plant tissue nutrients, aboveground biomass, and yield. Rhizosphere communities varied with rotation diversity and previous crop legacy. Concurrently, corn and soybean yields and biomasses were larger in more diverse rotations and with different crop legacies, but not tissue nutrients. Fungal communities predicted the suppression of corn seedlings when following soybean, and soybean seedlings when following corn, independently of rotation effects. This fungal effect ultimately predicted suppressed corn yield in the corn-soybean rotation, while in more diverse rotations, bacterial communities predicted corn would fully recover from a soybean legacy by flowering.