Abstract: Interactions between two species are often modified by other community members. Despite the prevalence of such interaction modifications, little is known about how they are linked to the temporal order of community assembly. Timing of species affects their pairwise interactions (i.e., priority effects) and should have the potential to affect interaction modifications in multispecies communities. Here, we use feedback between plants and soil microbiomes (plant-soil feedback) to examine how the germination phenology of plants influences interaction modifications. We build a mechanistic model with two processes that are well-supported by experiments but rarely explored in past models: first, we assume that the microbial dynamics operate at the same time scale as plant dynamics; second, we allow for each plant to cultivate the microbiome associated not only with itself but also other plants in the community. Using data generated by this mechanistic model, we first show that priority effects occur between two plants. We then develop a framework of time-dependent interaction modifications by extending a framework of pairwise priority effects. Finally, we add a third plant into the community and apply this framework to examine whether the third plant modifies the pairwise interaction and whether this modification depends on the germination phenology of the third plant. Applying our framework of time-dependent interaction modifications, we find that when a third plant is present in the community, both its presence and germination phenology modify the interaction between the other two plants. This time-dependent interaction modification is strongest when each plant can cultivate other plants’ associated microbiomes. Our findings suggest that time-dependent interaction modifications are likely widespread in multispecies communities and highlight the need of considering the timing of species' arrivals in diverse communities.
