Table 1.

Description of necessary criteria to demonstrate that plant–soil feedbacks are a stabilizing mechanism of coexistence.

criterion	description	evidence
1	negative PSF occurs and is caused by soil microbiota	species performance is reduced with its own soil microbes relative to those of its competitor(s)
2	negative frequency dependence occurs	per capita performance of a species declines as its relative frequency in the community increases; stronger effects with higher total plant density indicate strong competition
3	negative frequency dependence is stronger (or only occurs) in the presence of microbially driven PSF	declines in per capita performance as relative frequency increases are steeper in the presence of PSF than in its absence