Overestimated natural biological nitrogen fixation translates to an exaggerated CO2 fertilization effect in Earth system models

Thumbnail Image

Files

kou-giesbrecht-et-al-2025-overestimated-natural-biological-nitrogen-fixation-translates-to-an-exaggerated-co2.pdf (3.75 MB)

Access rights

openAccess
CC BY-NC-ND
publishedVersion

URL

Journal Title

Journal ISSN

Volume Title

A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
This publication is imported from Aalto University research portal.
View publication in the Research portal (opens in new window)
View/Open full text file from the Research portal (opens in new window)
Unless otherwise stated, all rights belong to the author. You may download, display and print this publication for Your own personal use. Commercial use is prohibited.

Authors

Date

2025-12-02

Department

Department of Built Environment

Major/Subject

Mcode

Degree programme

Language

en

Pages

11

Series

Proceedings of the National Academy of Sciences of the United States of America, Volume 122, issue 48, pp. e2514628122

Abstract

CO2 fertilization of the terrestrial biosphere is limited by nitrogen. Biological nitrogen fixation (BNF) is the dominant natural nitrogen source to the terrestrial biosphere and can alleviate nitrogen limitation but is poorly constrained in Earth system models (ESMs). Here, we compare terrestrial BNF from an ensemble of ESMs of the 6th Coupled Model Intercomparison Project to a new global synthesis of observations across natural and agricultural biomes. We find that compared to observations, ESMs underestimate agricultural BNF but overestimate natural BNF in the present day by over 50%. Natural BNF is overestimated in the most productive ecosystems that contribute most to the terrestrial carbon sink (forests and grasslands). ESMs with different BNF representations yield a range of BNF responses to CO2 enrichment. Some ESMs with phenomenological representations of BNF predict a natural BNF increase in response to a doubling of CO2 that aligns with a meta-analysis of CO2 enrichment experiments (31% increase) but fail to account for the substantial carbon cost of BNF. In contrast, ESMs with mechanistic representations of BNF account for its carbon cost as well as its regulation by nitrogen limitation but overestimate the BNF response to a doubling of CO2 (135% increase). Overall, all current BNF representations in ESMs fall short of fully capturing its response to rising atmospheric CO2. Finally, we find a positive correlation between modeled present-day natural BNF and the CO2 fertilization effect across ESMs, suggesting that overestimated natural BNF translates to an exaggerated CO2 fertilization effect of approximately 11% in ESMs.

Description

Keywords

CO2 fertilization, Earth system models, biological nitrogen fixation, CO fertilization

Other note

DOI

10.1073/pnas.2514628122

Citation

Kou-Giesbrecht, S, Reis Ely, C R, Perakis, S S, Cleveland, C C, Menge, D N L, Reed, S C, Taylor, B N, Batterman, S A, Crews, T E, Dynarski, K A, Gei, M, Gundale, M J, Herridge, D F, Jovan, S E, Peoples, M B, Piipponen, J, Rodríguez-Caballero, E, Salmon, V G, Soper, F M, Staccone, A P, Weber, B, Williams, C A & Wurzburger, N 2025, 'Overestimated natural biological nitrogen fixation translates to an exaggerated CO 2 fertilization effect in Earth system models', Proceedings of the National Academy of Sciences of the United States of America, vol. 122, no. 48, e2514628122, pp. e2514628122. https://doi.org/10.1073/pnas.2514628122

Permanent link to this item

https://urn.fi/URN:NBN:fi:aalto-202512028966

Collections

[article-cris] Insinööritieteiden korkeakoulu / ENG