Belowground competition can influence the evolution of root traits

Although root traits play a critical role in mediating plant-plant interactions and resource acquisition from the soil environment, research examining if and how belowground competition can influence the evolution of root traits remains largely unexplored. Here we examine the potential that root traits may evolve as a target of selection from interspecific competition using Ipomoea purpurea and I. hederacea, two closely related morning glory species that commonly co-occur in the United States as a model system. We show that belowground competitive interactions between the two species can alter the pattern of selection on root traits in each species. Specifically, competition with I. purpurea changes the pattern of selection on root angle in I. hederacea, and competitive interactions with I. hederacea changes the pattern of selection on root size in I. purpurea. However, we did not uncover evidence that intraspecific competition altered the pattern of selection on any root traits within I. hederacea. Overall, our results suggest that belowground competition between closely related species can influence the phenotypic evolution of root traits in natural populations. Our findings provide a microevolutionary perspective of how competitive belowground interactions may impact plant fitness, potentially leading to patterns of plant community structure.