The rhizosphere metabolome triggers species-specific and context-dependent root responses in later arriving plants

Priority effects can have long-lasting consequences for the structure and functioning of plant communities. Currently, it is poorly understood to what extent the rhizo-sphere metabolome of plant communities is conditioned by its species composition and whether these changes affect subsequent species during assembly. We collected soil solutions from plant communities differing in species and functional group composition (forbs or grasses). We evaluated the effect of the rhizosphere metabolome found in the soil solutions on the growth, biomass allocation, and functional traits of a forb (Dianthus deltoides) and a grass species (Festuca rubra). The rhizosphere metabolome of forb and grass communities differed in composition and chemical diversity. While F. rubra did not respond to different rhizosphere solutions, soil exploration by D. deltoides roots decreased when plants received the rhizosphere solution from a grass or a forb community. Structural equation modelling showed that reduced soil exploration by D. deltoides arose via either a root growth-dependent pathway (forb metabolome) or a root trait-dependent pathway (grass metabolome). Reduced soil exploration was not connected to a decrease in total N uptake. Our findings reveal that rhizosphere chemical cues can affect later arriving plants and create belowground priority effects in grasslands.