A plant carbon-nitrogen interface coupling framework in a coupled biophysical-ecosystem-biogeochemical model, SSiB version5/TRIFFID/DayCent-SOM: Its parameterization, implementation, and evaluation
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)
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.
SSiB5/TRIFFID/DayCent-SOM datasets for the paper's in-situ validations and global evaluations https://doi.org/10.5281/zenodo.7196869
Model code and software
SSiB Version5/TRIFFID/DayCent-SOM https://doi.org/10.5281/zenodo.7297108
Zheng Xiang et al.
Viewed (geographical distribution)
This work coupled the nitrogen model DayCent-SOM with the land surface moodel SSiB5/TRIFFID to study the N limitation on GPP,NPP and LAI. It is interesting to implement the carbon-nitrogen sutdy, which can be useful to earth system models or climate system models and it might improve the land-air interaction. The simulation with nitrogen shows the general better performance compared to that wihout N processes of SSiB4. But in some regions, such as Amazon and eastern China, the incorpoation of N limitation leads to larger underestimation of carbon fluxes, which is needed to more discussion the mechanism in science.