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 release N, we examined how interactions between their diversity and N addition affect Cannabis sativa growth. Microbiome predator addition overall boosted plant biomass by up to 53%, particularly under low N conditions, primarily by altering bacterial community composition and enriching functions related to carbon and N cycling. In turn, microbiome predator diversity had the strongest effect on biomass production, while N levels played a greater role in determining plant nutrient content. These findings suggest that increased microbiome predator diversity can reduce the plant’s dependency on added N, showing the pivotal role of soil biodiversity in enhancing plant performance and serving as tools to mitigate N inputs.