Decayeux et al. (2026) Representation of the nitrogen cycle and its coupling with the carbon cycle in ISBA (SURFEX v9) the land surface model: evaluation using two Free-Air CO 2 Enrichment experiment sites

Identification

• Journal: Geoscientific model development
• Year: 2026
• Date: 2026-08-21
• Authors: Jeanne Decayeux, Bertrand Decharme, Romain Darnajoux, Christine Delire
• DOI: 10.5194/gmd-19-7787-2026

Research Groups

• Météo-France, CNRS, Univ. Toulouse, CNRM
• Centre de Recherche sur la Biodiversité et l’Environnement (CRBE), Université de Toulouse, CNRS, IRD, Toulouse INP

Short Summary

This study presents the implementation of an explicit nitrogen cycle in the ISBA land surface model. The new version, called CN, is evaluated using data from two Free-Air CO2 Enrichment (FACE) experiment sites: Duke and Oak Ridge.

Objective

• To develop a process-based representation of the nitrogen cycle coupled with the carbon cycle in ISBA.
• To evaluate the impact of adding the nitrogen cycle on model performance at the FACE sites.

Study Configuration

• Spatial Scale: Local to regional scale, focusing on two specific sites: Duke and Oak Ridge.
• Temporal Scale: Long-term (10 years) simulations using daily time steps.

Methodology and Data

• Models used: ISBA land surface model with an explicit nitrogen cycle implementation.
• Data sources: FACE experiment data from Duke and Oak Ridge, including atmospheric CO2 concentrations, soil moisture, temperature, and carbon fluxes.

Main Results

• The CN version of the model shows improved performance compared to the C version, particularly in terms of net primary production (NPP) and nitrogen assimilation flux.
• The model reproduces well the main features of the nitrogen cycle at both sites, including nitrogen uptake, mineralization, and denitrification.

Contributions

• This study provides a process-based representation of the nitrogen cycle coupled with the carbon cycle in ISBA, which can be used to improve model performance and predict future climate change impacts.
• The results highlight the importance of considering nitrogen limitations on photosynthesis and decomposition processes in land surface models.

Funding

• This research was funded by the European Research Council (ERC) under grant agreement number 724263.

Citation

@article{Decayeux2026Representation,
  author = {Decayeux, Jeanne and Decharme, Bertrand and Darnajoux, Romain and Delire, Christine},
  title = {Representation of the nitrogen cycle and its coupling with the carbon cycle in ISBA (SURFEX v9) the land surface model: evaluation using two Free-Air CO 2 Enrichment experiment sites},
  journal = {Geoscientific model development},
  year = {2026},
  doi = {10.5194/gmd-19-7787-2026},
  url = {https://doi.org/10.5194/gmd-19-7787-2026}
}