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Title: Incorporating leaf chlorophyll content into a two-leaf terrestrial biosphere model for estimating carbon and water fluxes at a forest site

Abstract

Chlorophyll is the main light-harvesting pigment in leaves, facilitating photosynthesis and indicating the supply of nitrogen for photosynthetic enzymes. In this study, we explore the feasibility of integrating leaf chlorophyll content (Chl leaf) into a Terrestrial Biosphere Model (TBM), as a proxy for the leaf maximum carboxylation rate at 25 °C (V$$_{max}^{25}$$), for the purpose of improving carbon and water flux estimation. Measurements of Chl leaf and V$$_{max}^{25}$$ were made in a deciduous forest stand at the Borden Forest Research Station in southern Ontario, Canada, where carbon and water fluxes were measured by the eddy covariance method. The use of Chl leaf-based V$$_{max}^{25}$$ in the TBM significantly reduces the bias of estimated gross primary productivity (GPP) and evapotranspiration (ET) and improves the temporal correlations between the simulated and the measured fluxes, relative to the commonly employed cases of using specified constant V$$_{max}^{25}$$, leaf area index (LAI)-based V$$_{max}^{25}$$ or specific leaf area (SLA)-based V$$_{max}^{25}$$. The biggest improvements are found in spring and fall, when the mean absolute errors (MAEs) between modelled and measured GPP are reduced from between 2.2–3.2 to 1.8 g C m -2 d -1 in spring and from between 2.1–2.8 to 1.8 g C m -2 d -1 in fall. The MAEs in ET estimates are reduced from 0.7–0.8 mm d -1 to 0.6 mm d -1 in spring, but no significant improvement is noted in autumn. A two-leaf upscaling scheme is used to account for the uneven distribution of incoming solar radiation inside canopies and the associated physiological differences between leaves. We found that modelled V$$_{max}^{25}$$ in sunlit leaves is 34% larger than in the shaded leaves of the same Chl leaf, which echoes previous physiological studies on light acclimation of plants. This study represents the first case of the incorporation of chlorophyll as a proxy for V$$_{max}^{25}$$ in a two-leaf TBM at a forest stand and demonstrates the efficacy of using chlorophyll to constrain V$$_{max}^{25}$$ and reduce the uncertainties in GPP and ET simulations.

Authors:
 [1];  [1];  [1];  [2];  [3];  [4]
  1. Univ. of Toronto, Toronto, Ontario (Canada). Dept. of Geography and Planning
  2. Environment and Climate Change Canada, Toronto, Ontario (Canada). Climate Research Division
  3. Environment and Climate Change Canada, Toronto, Ontario (Canada). Air Quality Process Research Section
  4. North Michigan Univ., Marquette, MI (United States). Earth, Environmental and Geographical Sciences
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1567106
Grant/Contract Number:  
AC02-05CH11231
Resource Type:
Accepted Manuscript
Journal Name:
Agricultural and Forest Meteorology
Additional Journal Information:
Journal Volume: 248; Journal Issue: C; Journal ID: ISSN 0168-1923
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; cholorophyll; photosynthesis; terrestrial biosphere model; evapotranspiration; two-leaf scheme

Citation Formats

Luo, Xiangzhong, Croft, Holly, Chen, Jing M., Bartlett, Paul, Staebler, Ralf, and Froelich, Norma. Incorporating leaf chlorophyll content into a two-leaf terrestrial biosphere model for estimating carbon and water fluxes at a forest site. United States: N. p., 2018. Web. doi:10.1016/j.agrformet.2017.09.012.
Luo, Xiangzhong, Croft, Holly, Chen, Jing M., Bartlett, Paul, Staebler, Ralf, & Froelich, Norma. Incorporating leaf chlorophyll content into a two-leaf terrestrial biosphere model for estimating carbon and water fluxes at a forest site. United States. doi:10.1016/j.agrformet.2017.09.012.
Luo, Xiangzhong, Croft, Holly, Chen, Jing M., Bartlett, Paul, Staebler, Ralf, and Froelich, Norma. Mon . "Incorporating leaf chlorophyll content into a two-leaf terrestrial biosphere model for estimating carbon and water fluxes at a forest site". United States. doi:10.1016/j.agrformet.2017.09.012. https://www.osti.gov/servlets/purl/1567106.
@article{osti_1567106,
title = {Incorporating leaf chlorophyll content into a two-leaf terrestrial biosphere model for estimating carbon and water fluxes at a forest site},
author = {Luo, Xiangzhong and Croft, Holly and Chen, Jing M. and Bartlett, Paul and Staebler, Ralf and Froelich, Norma},
abstractNote = {Chlorophyll is the main light-harvesting pigment in leaves, facilitating photosynthesis and indicating the supply of nitrogen for photosynthetic enzymes. In this study, we explore the feasibility of integrating leaf chlorophyll content (Chlleaf) into a Terrestrial Biosphere Model (TBM), as a proxy for the leaf maximum carboxylation rate at 25 °C (V$_{max}^{25}$), for the purpose of improving carbon and water flux estimation. Measurements of Chlleaf and V$_{max}^{25}$ were made in a deciduous forest stand at the Borden Forest Research Station in southern Ontario, Canada, where carbon and water fluxes were measured by the eddy covariance method. The use of Chlleaf-based V$_{max}^{25}$ in the TBM significantly reduces the bias of estimated gross primary productivity (GPP) and evapotranspiration (ET) and improves the temporal correlations between the simulated and the measured fluxes, relative to the commonly employed cases of using specified constant V$_{max}^{25}$, leaf area index (LAI)-based V$_{max}^{25}$ or specific leaf area (SLA)-based V$_{max}^{25}$. The biggest improvements are found in spring and fall, when the mean absolute errors (MAEs) between modelled and measured GPP are reduced from between 2.2–3.2 to 1.8 g C m-2 d-1 in spring and from between 2.1–2.8 to 1.8 g C m-2 d-1 in fall. The MAEs in ET estimates are reduced from 0.7–0.8 mm d-1 to 0.6 mm d-1 in spring, but no significant improvement is noted in autumn. A two-leaf upscaling scheme is used to account for the uneven distribution of incoming solar radiation inside canopies and the associated physiological differences between leaves. We found that modelled V$_{max}^{25}$ in sunlit leaves is 34% larger than in the shaded leaves of the same Chlleaf, which echoes previous physiological studies on light acclimation of plants. This study represents the first case of the incorporation of chlorophyll as a proxy for V$_{max}^{25}$ in a two-leaf TBM at a forest stand and demonstrates the efficacy of using chlorophyll to constrain V$_{max}^{25}$ and reduce the uncertainties in GPP and ET simulations.},
doi = {10.1016/j.agrformet.2017.09.012},
journal = {Agricultural and Forest Meteorology},
number = C,
volume = 248,
place = {United States},
year = {2018},
month = {1}
}

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