Soil biodiversity may help cannabis grow with less fertilizer

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.