Summary
Tree health and fitness depend on the interactions among soil microbiota across space and time. Recent evidence, for instance, has shown that understanding the individual and interactive lifestyles of bacteria and ectomycorrhizal fungi (EcMF)—two of the most dominant and influential soil microbes in tree microbiomes—enhances our predictions of plant responses and ecosystem functions. The spatial features that shape the coexistence and plasticity of bacteria–EcMF interactions have long been a primary research interest and have therefore revealed key insights in the field. The temporal features of these interactions, however, have received considerably less attention, yet emerging evidence suggests that interactions at a particular time in space may have a disproportionate impact on the stability and outcome of relationships. In light of these observations, I outline bacteria–EcMF–tree interactions across the life cycle of EcMF and highlight the importance of ‘symbiosis critical points’ across developmental time, providing testable hypotheses and experimental frameworks that aim to advance the field moving forward. Though this viewpoint article focuses on the symbioses among these three organisms, the concepts, hypotheses, and frameworks presented herein extend to diverse multispecies systems.
