Microbe-mediated plant-soil feedback causes historical contingency effects in plant community assembly

Plant-soil feedback affects performance and competitive ability of individual plants. However, the importance of plant-soil feedback in historical contingency processes and plant community dynamics is largely unknown. In microcosms, we tested how six early-successional plant species of secondary succession on ex-arable land induced plant-specific changes in soil community composition. Following one growth cycle of conditioning the soil community, soil feedback effects were assessed as plant performance in soil of their own as compared to soil from a mixture of the other five early-successional species. Performance was tested in monocultures and in mixed communities with heterospecific competition from mid-successional species. The role of soil microorganisms was determined by isolating the microbial component from the soil community, re-inoculating microorganisms into sterilized substrate, and analyzing plant biomass responses of the early-and mid-successional species. Plant-soil feedback responses of the early-successional species were negative and significantly increased when the plants were grown in a competitive environment with he tero specifics. In monocultures, three early-successional species experienced negative feedback in soil with a history of conspecifics, while all early-successional species experienced negative feedback when grown with interspecific competition. Interestingly, the normative forb Conyza canadensis showed the weakest soil feedback effect. Biomass production of the early-successional plant species was profoundly reduced by the microbial inocula, most strongly when exposed to inocula of conspecific origin. Molecular characterization of the fungal and bacterial rhizosphere communities revealed a relationship between plant biomass production and the composition of the dominant fungal species. Furthermore, our results show that, in early secondary succession, the early-successional plant species induce changes in the soil microbial community composition that cause historical contingency effects in dominance patterns of mid-succession plant communities. We conclude that feedback between early-successional plant species and soil microorganisms can play a crucial role in breaking dominance of early-successional plant communities. Moreover the influences on soil microorganism community composition influenced plant community dynamics in the mid-successional plant communities. These results shed new light on how feedback effects between plants and soil organisms in one successional stage result in a biotic legacy effect, which influences plant community processes in subsequent successional stages.