Carbon and phosphorus exchange may enable cooperation between an arbuscular mycorrhizal fungus and a phosphate‐solubilizing bacterium

Summary Arbuscular mycorrhizal fungi (AMF) transfer plant photosynthate underground which can stimulate soil microbial growth. In this study, we examined whether there was a potential link between carbon (C) release from an AMF and phosphorus (P) availability via a phosphate‐solubilizing bacterium ( PSB ). We investigated the outcome of the interaction between the AMF and the PSB by conducting a microcosm and two Petri plate experiments. An in vitro culture experiment was also conducted to determine the direct impact of AMF hyphal exudates on growth of the PSB . The AMF released substantial C to the environment, triggering PSB growth and activity. In return, the PSB enhanced mineralization of organic P, increasing P availability for the AMF . When soil available P was low, the PSB competed with the AMF for P, and its activity was not stimulated by the fungus. When additional P was added to increase soil available P, the PSB enhanced AMF hyphal growth, and PSB activity was also stimulated by the fungus. Our results suggest that an AMF and a free‐living PSB interacted to the benefit of each other by providing the C or P that the other microorganism required, but these interactions depended upon background P availability.