Plant chemistry mediates interactions between plants and their environment. While intraspecific chemodiversity at the plant level is well-studied, the effects of groups of plants differing in chemistry on interactions need more attention. To test how intraspecific chemodiversity affects plant-arthropod interactions, we manipulated plots of Tanacetum vulgare L., differing in chemotype richness and composition. Over three seasons, we monitored four arthropod groups (herbivores, flower visitors, predators, and ants). We hypothesized that higher plot-level chemotype richness enhances occurrence across all studied arthropod groups and that the effect on abundance would be negative for herbivore and ant abundance and positive for flower visitors and predators. Mixed models revealed that with increasing plot-level chemotype richness, herbivore abundance decreased, flower visitor abundance increased, and predatory arthropods and ants remained largely unaffected. Specific chemotypes influenced community assembly within arthropod groups over time, emphasizing that plant chemical diversity shapes insect communities and contributes to ecosystem dynamics.

Plant-soil feedback is commonly pointed out as driver of plant community dynamics and species co-existence. However, experimental evidence for soil legacy effects of conditioning plant communities on responding plant communities under natural conditions is lacking. We conditioned 192 grassland plots with plant communities with different ratios of grasses and forbs and fast and slow-growing plants. Soil microbial legacies were most evident for soil fungi. Soil abiotic parameters did not change in response to conditioning. The soil legacies affected the composition of the succeeding vegetation. Plant communities of a specific functional type caused negative feedbacks on succeeding plants when they belonged to the same functional type. Richness, relative species cover and belowground biomass of the responding vegetation were all influenced by the growth rate of the conditioning community. We conclude that plant-soil feedbacks play an important role in vegetation assembly of natural communities.