EGUsphere EGUsphere EGUsphere EGUsphere Copernicus Publications Göttingen, Germany 10.5194/egusphere-2022-1111 A plant carbon-nitrogen interface coupling framework in a coupled biophysical-ecosystem-biogeochemical model, SSiB version5/TRIFFID/DayCent-SOM: Its parameterization, implementation, and evaluation Xiang Zheng 1 2 Xue Yongkang https://orcid.org/0000-0002-6169-9631 2 Guo Weidong https://orcid.org/0000-0003-0299-6393 1 4 Hartman Melannie D. 3 Liu Ye 2 5 Parton William J. 3 School of Atmospheric Sciences, Nanjing University, Nanjing, China Department of Geography, University of California, Los Angeles, CA 90095, USA Natural Resource Ecology Laboratory, Colorado State University, CO 80523, USA Joint International Research Laboratory of Atmospheric and Earth System Sciences, Nanjing, China Pacific Northwest National Laboratory, Richland, WA 99352, USA 07 11 2022 2022 1 43 Copyright: © 2022 Zheng Xiang et al. 2022 This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/ This article is available from https://egusphere.copernicus.org/preprints/2022/egusphere-2022-1111/ The full text article is available as a PDF file from https://egusphere.copernicus.org/preprints/2022/egusphere-2022-1111/egusphere-2022-1111.pdf

<p>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&ndash;2013 and global satellite-derived observations from 1948&ndash;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.</p>