Indirect interactions driven by soil effects enable coexistence among competing plant species

Reciprocal effects between plants and soil have been proposed as mechanisms that promote coexistence. However, recent theoretical and empirical works have questioned their role in stabilizing coexistence within multispecies communities. In these systems, indirect interactions mediated by plant-soil feedback may play a pivotal but often overlooked role. We investigate these indirect interactions using an experimental system of two competing shrub species grown in soil conditioned by a third tree species. Tree-induced shifts in soil microbial communities, metabolites, and nutrients boost growth in the weak competitor species while reducing germination in the dominant competitor. Simulations demonstrate that these shifts in plant performance are sufficient to stabilize coexistence and to closely reproduce natural spatial distribution patterns. Our findings underscore the role of plant-soil feedback in driving indirect interactions that sustain coexistence in diverse plant communities, highlighting the importance of indirect but also positive and negative multitrophic interactions in maintaining biodiversity.