Plants regulate the soil biodiversity–ecosystem stability relationship by mediating green‐brown food web coupling: Evidence from a removal experiment

Abstract Direct evidence of how plants regulate soil biodiversity–ecosystem stability relationships remains scarce, as the coupling between aboveground and belowground components makes it methodologically challenging to isolate plant‐mediated effects from the independent role of soil biota. Using a long‐term multifactorial semiarid grassland experiment with plant removal nested within grazing, nitrogen addition and water addition, we directly tested whether weakening plant‐derived green inputs reconfigures the soil biodiversity–ecosystem stability relationship through altered green‐brown food web coupling. By contrasting plant‐present and plant‐removal plots, we found that plants fundamentally reconfigured the biodiversity‐stability relationship. In the coupled state, plant presence shifted ecosystem stability towards biotic regulation: multifunctionality was supported by soil biota richness, while functional stability depended on biotic insurance via soil biota asynchrony and compositional stability. After plant removal, multifunctionality weakened and control shifted towards abiotic factors (soil pH/moisture); the observed increase in calculated stability reflected reduced temporal variability at a lower functional level rather than enhanced ecological resilience. Water availability was the strongest moderator of these plant‐mediated effects, whereas grazing primarily reduced the magnitude of multifunctionality and soil biota richness, and nitrogen addition had comparatively weak effects. Synthesis . Collectively, these findings provide direct experimental evidence that plants act as central hubs that reconfigure the biodiversity‐stability relationship by mediating green‐brown food web coupling, and emphasise that maintaining plant integrity is critical for sustaining high multifunctionality and biologically buffered stability under global change.