Nitrogen is an essential plant nutrient, and plant growth is regularly limited by short supplies of plant-available nitrogen — the nitrogen compounds that plants can use to grow — in the soil. Researchers often use the ratio of the stable isotopes nitrogen-15 and nitrogen-14 in plant tissue, expressed as a quantity known as δ15N, as an indicator of the availability of nitrogen in ecosystems1,2. Writing in Nature, Bassett et al.3 present an extensive set of measurements that reveal declines in δ15N across Swedish forests from 1961 to 2018. The findings support long-proposed theories that carbon dioxide-driven stimulation of tree growth could reduce soil nitrogen availability in terrestrial ecosystems1,2,4. The resulting shortage could constrain the ability of those ecosystems to sequester carbon in the future, meaning that larger reductions in fossil-fuel emissions than those currently projected would be needed to meet climate targets.
Nature 650, 560-561 (2026)
doi: https://doi.org/10.1038/d41586-026-00287-4
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Competing Interests The authors declare no competing interests.
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