Abstract
Biological nitrogen fixation (BNF) is the largest natural source of new nitrogen (N) that supports terrestrial productivity1,2, yet estimates of global terrestrial BNF remain highly uncertain3,4. Here we show that this uncertainty is partly because of sampling bias, as field BNF measurements in natural terrestrial ecosystems occur where N fixers are 17 times more prevalent than their mean abundances worldwide. To correct this bias, we develop new estimates of global terrestrial BNF by upscaling field BNF measurements using spatially explicit abundances of all major biogeochemical N-fixing niches. We find that natural biomes sustain lower BNF, 65 (52–77) Tg N yr−1, than previous empirical bottom-up estimates3,4, with most BNF occurring in tropical forests and drylands. We also find high agricultural BNF in croplands and cultivated pastures, 56 (54–58) Tg N yr−1. Agricultural BNF has increased terrestrial BNF by 64% and total terrestrial N inputs from all sources by 60% over pre-industrial levels. Our results indicate that BNF may impose stronger constraints on the carbon sink in natural terrestrial biomes and represent a larger source of agricultural N than is generally considered in analyses of the global N cycle5,6, with implications for proposed safe operating limits for N use7,8.
| Original language | English |
|---|---|
| Pages (from-to) | 705-711 |
| Number of pages | 7 |
| Journal | Nature |
| Volume | 643 |
| Issue number | 8072 |
| DOIs | |
| State | Published - Jul 17 2025 |
Funding
This paper is a contribution from a working group on BNF supported by the US Geological Survey (USGS) John Wesley Powell Center for Analysis and Synthesis (G19AC00036, S.S.P., D.N.L.M., C.C.C., S.C.R.). This research was supported in part by an appointment to the USGS Research Participation Program administered by the Oak Ridge Institute for Science and Education (ORISE) through an interagency agreement between the US Departments of Energy (DOE) and Interior (DOI) under DOE contract no. DE-SC0014664. D.N.L.M. was funded by the National Science Foundation (IOS-2129542). S.A.B. was funded by the Leverhulme Trust and the Natural Environment Research Council (NE/S009663/1 and NE/M019497/1). J.P. was funded by the European Research Council under the European Union’s Horizon 2020 Research and Innovation Programme (819202). E.R.-C. was supported by FEDER/Ministerio de Ciencia e Inovacion-Agencia Estatal de Investigación (PID2021-127631NA-I00 and RYC2020-030762-I). V.G.S. was supported by the U.S. Department of Energy Biological Environmental Research Program to UT-Battelle, LLC (DE-AC05-00OR22725) and the NGEE-Arctic project. This paper was reviewed by the USGS, USFS and USEPA for technical and policy content and approved for publication. The views and conclusions in this article represent those of USGS, and represent those solely of the authors from ORAU/ORISE, USFS and USEPA. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the US government. We thank C. Ely, K. Kavanagh, J. Larison, T. Greaver, A. Gray and M. Brehob. This paper is a contribution from a working group on BNF supported by the US Geological Survey (USGS) John Wesley Powell Center for Analysis and Synthesis (G19AC00036, S.S.P., D.N.L.M., C.C.C., S.C.R.). This research was supported in part by an appointment to the USGS Research Participation Program administered by the Oak Ridge Institute for Science and Education (ORISE) through an interagency agreement between the US Departments of Energy (DOE) and Interior (DOI) under DOE contract no. DE-SC0014664. D.N.L.M. was funded by the National Science Foundation (IOS-2129542). S.A.B. was funded by the Leverhulme Trust and the Natural Environment Research Council (NE/S009663/1 and NE/M019497/1). J.P. was funded by the European Research Council under the European Union’s Horizon 2020 Research and Innovation Programme (819202). E.R.-C. was supported by FEDER/Ministerio de Ciencia e Inovacion-Agencia Estatal de Investigación (PID2021-127631NA-I00 and RYC2020-030762-I). V.G.S. was supported by the U.S. Department of Energy Biological Environmental Research Program to UT-Battelle, LLC (DE-AC05-00OR22725) and the NGEE-Arctic project. This paper was reviewed by the USGS, USFS and USEPA for technical and policy content and approved for publication. The views and conclusions in this article represent those of USGS, and represent those solely of the authors from ORAU/ORISE, USFS and USEPA. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the US government. We thank C. Ely, K. Kavanagh, J. Larison, T. Greaver, A. Gray and M. Brehob.