Herbivory promotes more negative plant-soil feedbacks particularly for legumes and forbs

Abstract Purpose Plant-soil feedbacks and herbivory impact plant growth. We conducted a meta-analysis to test for an interaction between plant-soil feedbacks and herbivory, including effects on the magnitude and direction of feedbacks and the biomass or growth of herbivores. Methods Our literature search identified 244 studies to address our first question about herbivore impacts on plant-soil feedbacks as well as 179 studies to address our second question about plant-soil impacts on herbivores. We developed a database, calculated plant-soil feedback values for each study, then calculated Hedge’s D values for 1) the difference in plant-soil feedback values with and without herbivory for plants, and 2) the difference between home and away soils for insects. Results We found an overall significant weak negative effect of herbivory on plantsoil feedbacks, and effects differed between plant functional type. In legumes herbivory changed the outcome of plant-soil feedbacks from positive to negative, in forbs it further decreased negative feedbacks, and grasses were unaffected. We also found soil preconditioned in the lab produced consistently negative feedbacks whereas there was no significant change for soil preconditioned in the field. By contrast, there was no significant overall effect of plant-soil feedbacks on herbivores. Conclusion This first meta-analysis of the impact of herbivores on plant-soil feedbacks and vice versa identified an important potential role of plant functional type in determining the impact of conditioned soil on the magnitude and direction of feedbacks as well as some clear gaps that need to be addressed experimentally.