Plant-soil feedback: Conceptual integration and theoretical insights

Background/Question/Methods

The framework of plant-soil community feedback builds on the well established observation that plant species differ in their response to individual microbial species, as both the negative effects of individual species of soil pathogens and the positive effects of individual species of root symbionts are host-specific.  Growth rates of microbes are also host-specific and the composition of the soil community can change rapidly in response to plant identity.  This change in microbial composition will generate a feedback on plant relative performance which will define the long-term influence of soil microbes on plant competition.  Plant-soil feedback modeling conceptually integrates the effects of soil microbes into plant competition. A major strength of this approach is that the models are intimately linked to the set-up of pot experiments, enabling straightforward testing of theory with empirical data. Basic theory of plant-soil feedbacks demonstrates that negative plant-soil feedback can contribute to local scale coexistence, whereas positive feedback can contribute to local scale exclusion. An outstanding challenge, however, is the scaling of plant-soil feedback effects to the community level. Here, we present recent advances in modeling of plant-soil feedbacks, synthesizing how plant soil feedbacks may affect plant community dynamics.

Results/Conclusions

Working from basic principles, we define the critical metrics that determine the effect of soil community change on plant dynamics.  The critical metrics integrate across direct feedbacks of the soil community on the growth rates of conspecifics as well as indirect feedbacks through changes in growth rates of competitors.  We find that the expectation of negative feedback contributing to plant species coexistence holds regardless of the spatial scale of plant-microbe interactions or of dispersal, though the spatial scale does alter predicted spatial and numerical patterns.  For positive plant-soil feedback, however, we find that local-scale interactions and dispersal can lead to fundamentally different outcomes, with monotypic patches being stabilized and diversity being maintained across patches. The joint action of positive and negative feedbacks within a community can create context-dependent dynamics. These dynamics can result in transient, yet long-term divergence of community structure when communities vary in assembly history.