Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
Comment
. 2026 Jan 20;123(3):e2531787123.
doi: 10.1073/pnas.2531787123. Epub 2026 Jan 13.

Phantom sinks and missing pollution: Legacies of a hardened number

Bruce A Hungate  1   2
Affiliations
Comment

Phantom sinks and missing pollution: Legacies of a hardened number

Bruce A Hungate. Proc Natl Acad Sci U S A. .
No abstract available

PubMed Disclaimer

Conflict of interest statement

Competing interests statement:The author declares no competing interest.

Figures

Fig. 1.
Fig. 1.
Structural misallocation of biological nitrogen fixation (bar graph on Left) and its consequences (image on Right). The bar chart compares biological nitrogen fixation (BNF; Tg N y−1) from empirical estimates (black bars; Ely et al., as used by ref. 1) with CMIP6 model estimates (gray bars) for global, agricultural, and nonagricultural (“natural”) ecosystems. Global totals are similar, but models underestimate fixation in agriculture and overestimate fixation in natural ecosystems, so the spatial pattern is inverted. The central lens zooms from root nodules to the molecular scale of BNF: the enzyme nitrogenase converts inert atmospheric dinitrogen (N) into ammonium (NH+), the reduced nitrogen used for life. On the agricultural side of the landscape (Left), purple arrows trace “missing” fixed nitrogen that models omit, leaking as nitrate NO3−) to waters and as nitrous oxide (N2O) to the atmosphere. On the natural-ecosystem side (Right), cyan and white arrows show surplus modeled nitrogen that relaxes nitrogen limitation, inflates CO2 fertilization, and creates a phantom land carbon sink.
See this image and copyright information in PMC

Comment on

References

    1. Kou-Giesbrecht S., et al. , Overestimated natural biological nitrogen fixation translates to an exaggerated CO2 fertilization effect in Earth system models. Proc. Natl. Acad. Sci. U.S.A. 122, e2514628122 (2025). - PMC - PubMed
    1. Reis Ely C. R., et al. , Global terrestrial nitrogen fixation and its modification by agriculture. Nature 643, 705–711 (2025). - PMC - PubMed
    1. Cleveland C. C., et al. , Global patterns of terrestrial biological nitrogen (N2) fixation in natural ecosystems. Glob. Biogeochem. Cycles 13, 623–645 (1999).
    1. Ri X., Prentice I. C., Terrestrial nitrogen cycle simulation with a dynamic global vegetation model. Glob. Change Biol. 14, 1745–1764 (2008).
    1. Meyerholt J., Zaehle S., Smith M. J., Variability of projected terrestrial biosphere responses to elevated levels of atmospheric CO2 due to uncertainty in biological nitrogen fixation. Biogeosciences 13, 1491–1518 (2016).

LinkOut - more resources