Bedrock nitrogen weathering stimulates biological nitrogen fixation.

Global ecosystem models suggest that bedrock nitrogen (N) weathering contributes 10-20% of total N inputs to the natural terrestrial biosphere and >38% of ecosystem N supplies in temperate forests specifically. Yet, the role of rock N weathering in shaping ecological processes and biogeochemical fluxes is largely unknown. Here, we show that temperate forest ecosystems underlain by N-rich bedrock exhibit higher free-living N fixation rates than similar forests residing on N-poor parent materials, across sites experiencing a range of climate and tectonic regimes. This seemingly counterintuitive result can be explained by increased accumulation of soil C and P in high bedrock N sites, resulting in increased energy inputs and nutrient supplies to N fixing microorganisms. Our findings advance a novel ecosystem biogeochemical framework that recognizes long-term plant-soil-microbe feedbacks in shaping biogeochemical processes, with potentially widespread implications given the global distribution of bedrock N across Earth's terrestrial biomes.