Biotic and abiotic soil conditions are affected by plant species and can feed back to influence the performance of conspecific and heterospecific individuals. These plant–soil feedbacks have been shown to alter plant coexistence and biodiversity. Dominant species within biodiverse habitats may drive many of the plant-soil interactions, both biotic and abiotic, that promote the coexistence of many species. We investigated plant–soil feedbacks generated by a dominant, keystone bunchgrass, wiregrass (Aristida beyrichiana), in biodiverse longleaf pine (Pinus palustris) savannas of the southeastern U.S.A. To do so, we examined growth of wiregrass and another common bunchgrass, dropseed (Sporobolus junceus), in soil conditioned by wiregrass and soil collected away from wiregrass (>2m). To investigate effects of wiregrass ecotypic variation, soil samples and wiregrass seeds were collected from mesic and dry habitats. Dropseed were purchased from a local supplier. Finally, to detangle biotic and abiotic effects of plant–soil feedback we used live, sterile, and sterile soil inoculated with live soil. Plants were grown in a greenhouse for five months, after which we collected, dried, and weighed above- and belowground biomass. We compared log response ratios of all possible combinations of distance from wiregrass, seed and soil origin, and soil treatment.
Results/Conclusions
We found preliminary evidence of plant–soil feedbacks for both wiregrass and dropseed. Wiregrass collected from dry pine savannas had negative plant–soil feedback when grown in its origin soil. Growth responses were opposite depending on whether soil was collected directly under or away from other wiregrass: wiregrass had greater aboveground biomass in the inoculated compared to the sterile treatment when soil was collected away from wiregrass, while it had greater belowground biomass in the sterile compared to the inoculated treatment when soil was collected under wiregrass. No evidence of plant–soil feedback was found for individuals originating from mesic pine savannas. This suggests that biotic components of soil affect biomass production and that wiregrass likely has ecotypic variation between dry and mesic pine savannas. In contrast, dropseed belowground growth was affected by soil treatments when growing in mesic savanna. When compared to inoculated soil, belowground biomass of dropseed was greater in sterile soil, regardless of whether wiregrass conditioned the soil. When compared to inoculated soil, belowground biomass was lower in live wiregrass-conditioned soil. Our results indicated that plant–soil interactions related to its origins and ecotypic variation can determine plant responses to plant–soil feedback in longleaf pine savannas.