Artificial particles and soil communities interactively change heterospecific plant-soil feedbacks

Background and aims: Microplastics affect plant growth and change abiotic and biotic soil properties, such as soil structure and soil-community composition. However, how microplastics affect plant-soil interactions, such as plant-soil feedbacks (PSFs), is still poorly understood. Here, we tested how artificial particles affect heterospecific PSFs, depending on an intact or depleted soil community. Methods: We conducted a two-phase-greenhouse experiment using Centaurea jacea to condition soil containing an intact or initially depleted (by sterilization) soil community in the first phase. Subsequently, we grew individuals of Crepis biennis and Eragrostis minor in all combinations of soil conditioning (presence or absence of C. jacea in the first phase), soil-community status, and different material treatments including no added particles, glass particles, or three microplastics individually and mixed. Effects of soil community, material treatment and their interaction on PSFs were assessed based on plant biomass and root-morphology traits. Results: Particles in general, microplastics and glass, strengthened PSFs based on plant biomass. PSFs tended to be negative with the intact but positive with the initially depleted soil community. Overall, particle-addition effects on PSFs were stronger in the initially depleted community, indicating interactive effects of artificial particles in the soil and soil biota. Interactive particle and soil-community effects generally depended on material type and concentration. Conclusion: Our findings indicate that artificial particles can affect heterospecific PSFs and that these effects are likely to be partly mediated by the initial soil community. Further, they highlight the need for studies assessing potential ecological implications of microplastics on plant-soil interactions.