07 Nov 2022
 | 07 Nov 2022

A plant carbon-nitrogen interface coupling framework in a coupled biophysical-ecosystem-biogeochemical model, SSiB version5/TRIFFID/DayCent-SOM: Its parameterization, implementation, and evaluation

Zheng Xiang, Yongkang Xue, Weidong Guo, Melannie D. Hartman, Ye Liu, and William J. Parton

Abstract. Plant and microbial nitrogen (N) dynamics and N availability regulate the photosynthetic capacity and capture, allocation, and turnover of carbon (C) in terrestrial ecosystems. Studies have shown that a wide divergence in representations of N dynamics in terrestrial surface processes leads to large uncertainty in climate simulations and the projections of future trajectories. In this study, a plant C-N interface coupling framework was developed and implemented in a coupled biophysical-ecosystem-biogeochemical model (SSiB5/TRIFFID/DayCent-SOM). The main concept and structure of this plant C-N framework and its coupling methodology are presented. Different from many current approaches, this framework not only involves soil organic matter cycling, but uniquely takes into account plant N metabolism first, such as plant resistance and self-adjustment, which are represented by dynamic C / N ratios for each plant functional type (PFT). Then, when available N is less than plant N demand, N restricts plant growth, reducing gross primary productivity (GPP), and modulating plant respiration rates and phenology. All these considerations ensure a full incorporation of N regulations to plant growth and C cycling. This new approach has been tested to assess the effects of this coupling framework and N limitation on the terrestrial carbon cycle. Measurements from flux tower sites with different PFTs from 1996–2013 and global satellite-derived observations from 1948–2007 are used as references to assess the effect of the C-N coupling process on the long-term mean vegetation distribution and terrestrial C cycling using the offline SSiB5/TRIFFID/DayCent-SOM model, which use observed meteorological forcing to drive the model. The sensitivity of the terrestrial C cycle to different components in the framework is also assessed. The results show a general improvement with the new plant C-N coupling framework, with more consistent emergent properties, such as GPP, leaf area index (LAI), and respiration, compared to observations. The main improvements occur in tropical Africa and boreal regions, accompanied by a decrease of the bias in global GPP and LAI by 16.3 % and 27.1 %, respectively.

Zheng Xiang et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-1111', Anonymous Referee #1, 04 Jan 2023
    • AC1: 'Reply on RC1', Zheng Xiang, 19 Mar 2023
  • RC2: 'Comment on egusphere-2022-1111', Anonymous Referee #2, 10 Jan 2023
    • AC2: 'Reply on RC2', Zheng Xiang, 19 Mar 2023

Zheng Xiang et al.

Data sets

SSiB5/TRIFFID/DayCent-SOM datasets for the paper's in-situ validations and global evaluations Yongkang Xue; Zheng Xiang

Model code and software

SSiB Version5/TRIFFID/DayCent-SOM Zheng Xiang

Zheng Xiang et al.


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Short summary
A process-based plant Carbon (C)-Nitrogen (N) interface coupling framework has been developed, which mainly focuses on the plant resistance and N limitation effects on photosynthesis, plant respiration, and plant phenology. A dynamic C / N ratio is introduced to represent plant resistance and self-adjustment. The framework has been implemented in a coupled biophysical-ecosystem-biogeochemical model and testing results show a general improvement in simulating plant properties with this framework.