How biodiversity affects terrestrial productivity is important to the maintenance of ecosystem services under global change. Although the crucial role of plant-soil feedbacks (PSF) in determining diversity-productivity relationship has been increasingly recognized in recent years, its legacy effects on subsequent diversity-productivity relationship are still unclear.

We conducted a classic PSF experiment to assess how plant diversity-conditioned soils influenced subsequent plant diversity-productivity relationships, where three plant diversity levels (1, 4, and 8 species) were planted in soils conditioned at three diversity levels (conditioned by 1, 4, and 8 species for 3 years). In addition, to test the role of soil microbial diversity in mediating the effects of soil conditioning diversity, the three plant diversity levels were planted with low, moderate, and high soil biodiversity created by a soil inoculum dilution.

The results showed that plant productivities were promoted by mixed-conditioned soils (4 and 8 species) compared to mono-conditioned soils (1 species). Productivity was positively related to planted diversity in mixed-conditioned soils, while showing no relation to planted diversity in mono-conditioned soils. Productivity was promoted by soil biodiversity when 4 and 8 species were mixed planted, while it did not change when 1 species was planted. 

Synthesis and applications. Our results highlight that PSF is crucial to strengthening the positive effects of biodiversity on productivity, implying that diversifying cropping systems should be encouraged in agroecosystem management to benefit from positive PSF effects. The importance of soil legacy for optimizing plant productivity is particularly important for conditioning soils with an intermediate number of plant species.