Vegetation clumping modulates global photosynthesis through adjusting canopy light environment

Journal Article · 07 November 2022 · Global Change Biology

DOI: https://doi.org/10.1111/gcb.16503 · OSTI ID:1897536

Li, Fa  ^[1]; Hao, Dalei  ^[2]; Zhu, Qing  ^[3]; Yuan, Kunxiaojia  ^[3]; Braghiere, Renato K.  ^[4]; He, Liming  ^[5]; Luo, Xiangzhong  ^[6]; Wei, Shanshan  ^[7]; Riley, William J.  ^[3]; Zeng, Yelu  ^[1]; Chen, Min  ^[1]

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1. Department of Forest and Wildlife Ecology University of Wisconsin‐Madison Madison Wisconsin USA
2. Atmospheric Sciences and Global Change Division Pacific Northwest National Laboratory Richland Washington USA
3. Climate and Ecosystem Sciences Division, Climate Sciences Department Lawrence Berkeley National Laboratory Berkeley California USA
4. Division of Geological and Planetary Sciences California Institute of Technology Pasadena California USA, Jet Propulsion Laboratory California Institute of Technology Pasadena California USA
5. Canada Centre for Mapping and Earth Observation Natural Resources Canada Ottawa Ontario Canada
6. Department of Geography National University of Singapore Singapore Singapore
7. Centre for Remote Imaging, Sensing and Processing National University of Singapore Singapore Singapore

Abstract The spatial dispersion of photoelements within a vegetation canopy, quantified by the clumping index (CI), directly regulates the within‐canopy light environment and photosynthesis rate, but is not commonly implemented in terrestrial biosphere models to estimate the ecosystem carbon cycle. A few global CI products have been developed recently with remote sensing measurements, making it possible to examine the global impacts of CI. This study deployed CI in the radiative transfer scheme of the Community Land Model version 5 (CLM5) and used the revised CLM5 to quantitatively evaluate the extent to which CI can affect canopy absorbed radiation and gross primary production (GPP), and for the first time, considering the uncertainty and seasonal variation of CI with multiple remote sensing products. Compared to the results without considering the CI impact, the revised CLM5 estimated that sunlit canopy absorbed up to 9%–15% and 23%–34% less direct and diffuse radiation, respectively, while shaded canopy absorbed 3%–18% more diffuse radiation across different biome types. The CI impacts on canopy light conditions included changes in canopy light absorption, and sunlit–shaded leaf area fraction related to nitrogen distribution and thus the maximum rate of Rubisco carboxylase activity ( V _cmax ), which together decreased photosynthesis in sunlit canopy by 5.9–7.2 PgC year ⁻¹ while enhanced photosynthesis by 6.9–8.2 PgC year ⁻¹ in shaded canopy. With higher light use efficiency of shaded leaves, shaded canopy increased photosynthesis compensated and exceeded the lost photosynthesis in sunlit canopy, resulting in 1.0 ± 0.12 PgC year ⁻¹ net increase in GPP. The uncertainty of GPP due to the different input CI datasets was much larger than that caused by CI seasonal variations, and was up to 50% of the magnitude of GPP interannual variations in the tropical regions. This study highlights the necessity of considering the impacts of CI and its uncertainty in terrestrial biosphere models.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States); Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
• Sponsoring Organization: National Aeronautics and Space Administration (NASA); National Science Foundation (NSF); USDA; USDOE; USDOE Office of Science (SC), Biological and Environmental Research (BER)
• Grant/Contract Number: AC02-05CH11231; AC05-76RL01830
• OSTI ID: 1897536
• Report Number(s): PNNL-SA-174765
• Journal Information: Global Change Biology, Journal Name: Global Change Biology Journal Issue: 3 Vol. 29; ISSN 1354-1013
• Publisher: Wiley-BlackwellCopyright Statement
• Country of Publication: United Kingdom
• Language: English