Plant-soil feedbacks in a diverse grassland: Soil remembers, but not too much

1. Plant-soil feedbacks (PSFs) are one of the major drivers of species coexistence in highly dynamic and low-diversity communities, such as early successional stands or agricultural systems. However, in stable and species-rich communities, PSFs are much more complex because of numerous species interactions. In this study, we aimed to reveal if PSFs of a dominant species can be detected within a diverse plant community and to what extent they can be influenced by the effects of co-occurring species.2. We investigated PSFs between a dominant grass, Festuca rubra, and three other species from a species-rich mountain grassland, taking advantage of the 18-year field removal experiment. We tested whether such a long-term presence/absence of Festuca can shape the feedback of the grassland community and whether these effects prevail in the lower soil layer, where Festuca roots are relatively more abundant, compared to the upper soil layer. We evaluated how experimentally induced soil legacies of Festuca in a pot experiment are modified by subsequently grown plants, both at the level of plant responses and changes in abiotic and biotic soil properties.3. At the level of the entire community, the soil legacies of the dominant Festuca were not detectable. However, the responses of the plants differed between the soil samples from the upper and lower soil layer. The pot experiment showed that the soil legacies of subsequently growing plants interact, influencing soil properties as well as plant responses to these altered soils. Generally, we found a stronger signal of the most recent conditioning, although the effect of the first conditioning plant was still detectable in many of the measured variables. Plant biomass in the feedback phase was mainly linked to the levels of plant-available soil nitrogen, although it was also affected by the composition of microbial communities.4. Synthesis. We showed that plant-induced soil legacies can be altered by legacies of co-occurring species, complicating plant-soil feedbacks in diverse communities. Despite the detectable legacy effects on final plant biomass, in the short term, plant growth responds more strongly to the levels of available nutrients. We also highlight the vertical distribution of plant-soil feedbacks.