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Isotopic evidence for oligotrophication of terrestrial ecosystems



Human societies depend on an Earth system that operates within a constrained range of nutrient availability, yet the recent trajectory of terrestrial nitrogen (N) availability is uncertain. Examining patterns of foliar N concentrations and isotope ratios (δ15N) from more than 43,000 samples acquired over 37 years, here we show that foliar N concentration declined by 9% and foliar δ15N declined by 0.6–1.6‰. Examining patterns across different climate spaces, foliar δ15N declined across the entire range of mean annual temperature and mean annual precipitation tested. These results suggest declines in N supply relative to plant demand at the global scale. In all, there are now multiple lines of evidence of declining N availability in many unfertilized terrestrial ecosystems, including declines in δ15N of tree rings and leaves from herbarium samples over the past 75–150 years. These patterns are consistent with the proposed consequences of elevated atmospheric carbon dioxide and longer growing seasons. These declines will limit future terrestrial carbon uptake and increase nutritional stress for herbivores.

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The data sets generated during and/or analysed during the current study are available in the Dryad repository ( All codes used for statistical analyses and figure generation are available on Dryad (

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Funding for this research was in part provided by the BRIDGE Project (ANR-2006 Biodiversity Call) and from an ‘Investissement d’Avenir’ grant managed by the Agence Nationale de la Recherche (CEBA, grant no. ANR-10-LABX-0025) (J.C.R.); by the European Research Council through the Advanced Grant Project TREEPEACE (grant no. FP7-339728) and the Cluster of Excellence COTE (grant no. ANR-10-LABX-45) (S.D.); by NASA project no. NNX12AK56G and EU MSCA individual fellowship (project no. 705432) (R.G.); by COILEX (grant no. CGL2008-01671), ECOLPIN (grant no. AGL2011-24296) and EU MSCA individual fellowship (project no. 750252) (S.M.J.); and by the Russian Science Foundation (grant no. 16-14-10208) (M.M.). No funding was provided to J.M.C. or A.J.E. in support of this research.

Author information

J.M.C. and A.J.E. conceived of the research, conducted analyses, generated figures and prepared the original draft. All authors contributed data and provided comments on manuscripts.

Competing interests

Although J.M.C. is an owner of Jonah Ventures, a for-profit DNA sequencing company, the authors declare no competing interests in the publication of this research.

Correspondence to Joseph M. Craine.

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Fig. 1: Relationships between residual foliar δ15N of non-N2-fixing species and predictors.
Fig. 2: Results of the regressions of residual foliar δ15N and residual log-transformed foliar [N].
Fig. 3: Conceptual diagram summarizing N availability bifurcation hypothesis for global terrestrial ecosystems.