Feedback in the plant-soil system

Feedback between plants and the soil is frequently invoked on the basis of evidence of mutual effects. Feedback can operate through pathways involving soil physical properties, chemical and biogeochemical properties and processes, and biological properties, including the community composition of the microbiota and soil fauna. For each pathway, we review the mechanistic basis and assess the evidence that feedback occurs. We suggest that several properties of feedback systems (for example, their complexity, specificity, and strength relative to other ecological factors, as well as the temporal and spatial scales over which they operate) be considered. We find that the evidence of feedback is strongest for plants growing in extreme environments and for plant-mutualist or plant-enemy interactions. We conclude with recommendations for a more critical appraisal of feedback and for new directions of research.