Evidence for Elton’s diversity-invasibility hypothesis from belowground

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.