Soil Microbiome Predator Diversity Outperforms Nitrogen Addition in Boosting Plant Biomass via Bacterial Community Shifts

Nitrogen (N) is crucial for plant growth, but its overuse harms biodiversity. Increasing soil biodiversity might provide the means to reduce N inputs, but experimental evidence for this paradigm shift is limited. Using microbiome predators (protists and nematodes) that shape microbiome composition and participate in N cycling, we examined how interactions between their diversity and N addition affect Cannabis sativa growth. The addition of microbiome predators increased plant biomass by up to 53%, irrespective of diversity level, with effects reaching up to 60% under higher microbiome predator diversity. This biomass increase was primarily associated with changes in bacterial community composition and enriching functions related to carbon and N cycling. In contrast, N input played a greater role in determining plant and soil nutrient content. These findings suggest that microbiome predators determine plant biomass in a diversity and N-specific manner, showing the pivotal role of soil biodiversity in enhancing plant performance and serving as promising tools to mitigate N inputs.