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Nitrogen (N) limits the productivity of many ecosystems worldwide, thereby restricting the ability of terrestrial ecosystems to offset the effects of rising atmospheric CO₂ emissions naturally^,. Understanding input pathways of bioavailable N is therefore paramount for predicting carbon (C) storage on land, particularly in temperate and boreal forests^,. Paradigms of nutrient cycling and limitation posit that new N enters terrestrial ecosystems solely from the atmosphere. Here we show that bedrock comprises a hitherto overlooked source of ecologically available N to forests. We report that the N content of soils and forest foliage on N-rich metasedimentary rocks (350–950 mg N kg⁻¹) is elevated by more than 50% compared with similar temperate forest sites underlain by N-poor igneous parent material (30–70 mg N kg⁻¹). Natural abundance N isotopes attribute this difference to rock-derived N: ¹⁵N/¹⁴N values for …