Expanded trade: tripartite interactions in the mycorrhizosphere

Interactions between arbuscular mycorrhizal fungi (AMF), plants, and the soil microbial community have the potential to increase the availability and uptake of phosphorus (P) and nitrogen (N) in agricultural systems. Nutrient exchange between plant roots, AMF, and the adjacent soil microbes occurs at the interface between roots colonized by mycorrhizal fungi and soil, referred to as the mycorrhizosphere. Research on the P exchange focuses on plant-AMF or AMF-microbe interactions, lacking a holistic view of P exchange between the plants, AMF, and other microbes. Recently, N exchange at both interfaces revealed the synergistic role of AMF and bacterial community in N uptake by the host plant. Here, we highlight work carried out on each interface and build upon it by emphasizing research involving all members of the tripartite network. Both nutrient systems are challenging to study due to the complex chemical and biological nature of the mycorrhizosphere. We discuss some of the effective methods to identify important nutrient processes and the tripartite members involved in these processes. The extrapolation of in vitro studies into the field is often fraught with contradiction and noise. Therefore, we also suggest some approaches that can potentially bridge the gap between laboratory-generated data and their extrapolation to the field, improving the applicability and contextual relevance of data within the field of mycorrhizosphere interactions. Overall, we argue that the research community needs to adopt a holistic tripartite approach and that we have the means to increase the applicability and accuracy of in vitro data in the field.