Growing evidence suggests that plant-soil microbe interactions have important implications for plant community composition. Recent studies of plant-soil feedbacks, where plants influence the soil and the success of subsequent plants grown in that soil, suggest that plant species identity strongly influences these feedbacks. Such studies often compare effects of conspecific to heterospecific soils, and heterospecific species are not all created equal. Closely related species might have similar soil microbes, for example, if they share soil mutualists or pathogens. Alternatively, closely related plants might have very different effects on soil microbes, for example, if close relatives occur in different habitat types. However, when and in what direction, phylogeny influences plant-soil microbe interactions is poorly understood. We combined experimental tests with molecular characterization of the soil microbial community to test for effects of soil biota and phylogeny on plant performance. For example, we hypothesized that if soil pathogens are shared by close relatives, that plants might be suppressed by soils conditioned by their close relatives. Further, we conducted a literature review to identify knowledge gaps in our understanding of the role of phylogeny in plant-soil microbe interactions.
Results/Conclusions
Molecular characterization of the field soil microbial communities of 14 plant species found that plant genus explained a significant amount of the variance in soil fungal community composition. This implicates phylogeny, as well as plant species identity, soil chemistry, and spatial location, as factors explaining soil microbial communities in the plant rhizosphere. In a greenhouse experiment, Aquilegia canadensis performed better in soils conditioned by distant relatives’ soils than in close relatives' soils, and this effect disappeared with soil sterilization, consistent with closely related plants sharing soil pathogens or having similar responses to pathogens. A literature review points to a particular dearth of studies that include conspecific soils from both the native and introduced range, and more such studies would test the Enemy Escape hypothesis for soil microbial communities. More studies are needed that incorporate phylogeny in their experimental design to determine what factors influence phylogenetic patterns for plant-soil feedbacks and plant-soil microbe interactions.