Species-level studies do not upscale to community-wide plant-soil feedbacks

Soil legacy effects of plants (i.e., plant-soil feedback, PSF) are key drivers of the maintenance of biodiversity and alien plant invasion. While most research (88.9% of 460 experiments) has focused on PSFs of single-species, we showed that 4.6 (on average) herbaceous species co-occur and likely to interact belowground and collectively shaping plant-soil interactions across ~2000 0.25 m2 plots (only 0.03% hosting a single species) in a field survey of herbaceous plant communities in East China. However, can species-level PSFs directly translate to community-level PSFs remains untested. We experimentally showed that rhizosphere fungal communities of three species were significantly influenced by neighbouring species diversity, rather than just focal species itself. A two-phase PSF experiment further showed that, when the soil was conditioned by more than four species, community-level PSFs were disproportionately influenced by specific species rather than being a simple additive contribution from single-species PSFs. This inequality was more pronounced with increasing species richness. These findings highlight the importance of prioritizing research on community-level PSFs, particularly in species-rich ecosystems, which may reshape our understanding on plant-soil interactions and their role in shaping plant community dynamics.