Aboveground-belowground microbial interactions in plants: A call to recognize the complexity within multispecies...

Understanding and predicting plant responses to biotic and abiotic environments necessitates grappling with thousands of microbial interactions occurring within aboveground and belowground plant tissues. These distinct microbial communities are indirectly connected through their plant hosts, and aboveground-belowground (AGBG) microbial interactions could play large roles in plant health and drive plant community and ecosystem-level responses. In this review and synthesis, we first discuss mechanisms through which focal microbes directly and indirectly affect other microbes in distal plant compartments. We then add in a layer of complexity: How might microbial community interactions within aboveground plant organs affect root-associated microbiomes, and vice versa? We point to gaps in our knowledge that should drive future research agendas on how "discrete" microbial communities within plants influence one another-a key feature currently missing in plant microbiome research. We also discuss the utility of applying existing ecological theory to enhance the predictive power of plant microbiome research, particularly regarding the outcomes of AGBG microbial interactions across diverse environmental and ecological contexts. These efforts will be especially important within fields such as sustainable agriculture that seek to harness plant-microbiome interactions within a changed and ever-changing world.