Intra-trophic microbial associations bridge metallic micronutrients and ecosystem multifunctionality

The role of metallic micronutrients in regulating the soil microbiome and ecosystem multifunctionality is virtually unknown, limiting our ability to predict the future sustainability of terrestrial ecosystems under global change. Here we conducted a standardized field survey across China with 261 soil samples to investigate how metallic micronutrients (Fe, Mn, Cu, Zn, Mo, Ni) shape ecosystem multifunctionality. Our results revealed that bacterial communities were more sensitive to metallic microelements than eukaryotic groups (including fungi, protozoa, nematodes, and invertebrates). Although soil biodiversity exhibited taxa-specific responses to microelements, only available Zn consistently enhanced biodiversity of the overall community. Metallic micronutrients regulated ecosystem multifunctionality through dual mechanisms within microbial networks: promoting functioning by enhancing connectivity within trophic levels, yet suppressing it by reducing dominant phyla. This establishes intra-trophic networks as the key bridge linking micronutrient availability to multifunctionality. Together, these findings provide a mechanistic understanding essential for predicting and managing soil health in the face of changing micronutrient availability.