The ERI model: A novel framework for evaluating plant-soil feedbacks among multiple competing species

12 April 2019

Xiao, Sa; Atwater, Dan; Callaway, Ragan M.

Plant-soil feedbacks have important effects on plant communities, but most theory has been derived from experiments on intraspecific plant-soil feedbacks. Much less is known about how interspecific plant-soil feedbacks affect coexistence and plant communities, due in part to experimental and analytical challenges. Here, we propose a framework for evaluating plant-soil feedbacks among multiple interacting species that incorporates 1) the average effect each species has on conspecific and heterospecific neighbors via how they modify soil biota, 2) the average response of each species to the soil modifications made by neighboring species, and 3) intraspecific feedback. We refer to this as the “Effect-Response-Intraspecific” (ERI) model. We used individual-based models to evaluate the relative importance of intraspecific and interspecific soil feedback in determining species abundance ranks in simulated plant communities. To compare the heuristic value of the ERI model to that of an established model in which effects and responses to soil feedback are not explicitly recognized, we evaluated a “full-factorial” model in which soil feedbacks among five plant species were measured and then explicitly modeled. The ERI model indicated that the response to interspecific plant-soil feedbacks was the key factor for species’ abundance rank without spatial structure. In contrast, interspecific plant soil feedback had no impact on species abundance with spatial structure, and intraspecific feedback became dominant. Thus, our models predict that the relative importance of intraspecific and interspecific feedbacks changes as a function of the degree of spatial structure in a system. Overall, the ERI model provides a novel and tractable framework for evaluating complex multi-species plant-soil feedbacks.