Grassland degradation alters plant and soil biodiversity-multifunctionality relationships

Biodiversity is known to promote ecosystem multifunctionality (EMF), but how grassland degradation influences the relationship between biodiversity and EMF remains unclear. Using paired observations at 44 sites (a total of 792 sampling quadrats) along a 2600 km transect, we tested how moderate grassland degradation influenced 20 surrogates of ecosystem functions, EMF, plant richness, soil bacteria, fungi and protist richness, and biodiversity-EMF relationships in Tibetan alpine grasslands. Our results reveal significant declines in individual ecosystem functions and EMF with moderate grassland degradation. In contrast, both plant richness and integrated soil biodiversity exhibit significant increases. Further analyses using structural equation models demonstrate that following degradation, the effect of soil biodiversity on EMF strengths, whereas that of plant richness weakens. These findings offer large-scale empirical evidence that moderate grassland degradation can amplify both soil biodiversity and its functional importance, emphasizing the key role of belowground biodiversity in supporting ecosystem functioning in degraded grasslands.