Root exudates drive interspecific facilitation by enhancing nodulation and N 2 fixation

Significance Plant diversity often leads to an increase in ecosystem productivity, but the underpinning mechanisms remain poorly understood. We found that faba bean/maize intercropping enhances productivity, nodulation, and N 2 fixation of faba bean through interspecific root interactions. We provide a mechanism explaining how maize promotes N 2 fixation of faba bean, where root exudates from maize increase root hair deformation and nodulation in faba bean, double exudation of flavonoids (signaling compounds for rhizobia), and up-regulate the expression of a chalcone–flavanone isomerase gene involved in flavonoid synthesis, and genes mediating nodulation and auxin responses. Our results provide a mechanism for facilitative root–root interactions explaining how species diversity may enhance ecosystem productivity with important implications for developing sustainable agriculture.