Why, when, and how microbes can benefit ecological restorations: current approaches and future directions

The restoration of terrestrial ecosystems often requires the reestablishment of plant communities, but restorations often overlook microbial communities, which directly and indirectly structure plant diversity. Legacies of anthropogenic disturbance radically alter microbial diversity and, contrary to previous assumptions, the natural recovery of microbial communities is not guaranteed, even after decades. This necessitates established and novel forms of microbial restoration, such as the addition of key microbial taxa to boost plant diversity and ecosystem functioning. Here, we review why anthropogenically disturbed microbial communities need restoration, the positive outcomes of doing so for plant conservation, community dynamics, and ecosystem functioning, and best practices when taking these approaches. We also highlight knowledge gaps in this emerging field, such as the mechanisms underlying successful microbially based restoration of plant communities, how shifting climate conditions will impact global microbiomes, and the potential for off-target effects. Our goal is to shift the perspective of microbes as passive measures of restoration success to the restoration of microbial communities as a major objective and driver of restoration outcomes.