Legume-Mediated Soil Legacy Effects Strengthen Plant Diversity-Productivity Relationships

Abstract Although the crucial role of plant-soil feedback (PSF) associated with species composition in determining diversity-productivity relationships has been increasingly recognized, its legacy effects on subsequent diversity-productivity relationships remain unclear. We conducted a classic PSF experiment to assess how conditioning diversity and species composition shape subsequent diversity-productivity relationships. Plant communities at four diversity levels (1, 2, 4, and 8 species) were grown in soils previously conditioned at matching diversity levels and one of five species compositions. Additionally, to test whether soil microbial diversity mediates composition effects, the same communities were grown under low, moderate, and high soil biodiversity generated via inoculum dilution. Productivity was higher on legume-conditioned soils than on non-legume soils. Legumes also steepened the diversity-productivity relationship, with the strongest responses following monoculture conditioning. Synthesis. In addition to plant diversity, species composition also shapes soil legacy effects, especially for specific plant functional groups such as legumes. Under the same plant diversity, the extent of soil legacy effects on succeeding plants depended on species composition, particularly under low diversity, and likely promoted subsequent community growth by enhancing nutrient availability and microbial diversity. Our findings highlight that manipulating species composition, particularly the inclusion of legumes, can harness soil legacy effects to enhance ecosystem productivity in ecological agriculture.