Sixty year ago, Charles Elton posed that species-rich communities should be more resistant to biological invasion. However, still little is known about which processes could drive the diversity-invasibility relationship. Here we examined whether soil-microbes-mediated apparent competition on alien invaders is more negative when the soil originates from multiple native species. We trained soils with five individually grown native species, and used amplicon sequencing to analyze the resulting bacterial and fungal soil communities. We mixed the soils to create trained soils from one, two or four native species. We then grew four alien species separately on these differently trained soils. In the soil-conditioning phase, the five native species built species-specific bacterial and fungal communities in their rhizospheres. In the test phase, it did not matter for biomass of alien plants whether the soil had been trained by one or two native species. However, the alien species achieved 11.7% (95% CI: 3.7% ~ 20.1%) less aboveground biomass when grown on soils trained by four native species than on soils trained by two native species. Our results revealed soil-microbes-mediated apparent competition as a mechanism underlying the negative relationship between diversity and invasibility.

We conducted an experiment with five native plant species and four alien plant species to test whether the diversity-invasibility relationship may be mediated by soil microbes. We first grew each of the five native species individually to train soils. Then in a second phase, we mixed soil samples from one, two or four native species, and grew one of the four alien species on the soil mixture. we additionally created soil mixtures for single native species from one, two or four different individuals, and then grew one of the four alien species on the soil mixture.

see 'readme' for how to use this dataset.