Analyses of canopy photosynthesis derived from three-dimensional model simulations of sun-induced chlorophyll fluorescence

Gao, Sicong

Analyses of canopy photosynthesis derived from three-dimensional model simulations of sun-induced chlorophyll fluorescence

Gao, Sicong

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Publication Type:: Thesis
Issue Date:: 2020

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Field	Value	Language
dc.contributor.author	Gao, Sicong
dc.date.accessioned	2020-05-03T23:09:18Z
dc.date.available	2020-05-03T23:09:18Z
dc.date.issued	2020
dc.identifier.uri	http://hdl.handle.net/10453/140431
dc.description	University of Technology Sydney. Faculty of Science.	en_AU
dc.description.abstract	Recently, measurements of sun-induced chlorophyll fluorescence (SIF) has become a new approach to estimate vegetation photosynthetic activity and detect vegetation stress. However, the environmental factors controlling SIF largely remain unknown for different vegetation biome types. In addition, SIF measured at the top of canopy (TOC) is confounded by interactions between solar radiation and vertical canopy structures. Hence, development of three-dimensional (3-D) radiative transfer models, capable of simulating SIF, would be of immense benefit to test and verify various hypothesises. The goal of this thesis is to develop a new 3-D SIF model and apply it to assess the relationship between SIF and plant photosynthetic activity across different spatial and temporal scales. Specifically, I (1) developed a new SIF module for FLiES (Forest Light Environmental Simulator) model (FLiES-SIF) and validated it with SIF observations at the seasonal scale; (2) partitioned SIF signals to overstory and understory layers by using FLiES-SIF, and then analysed the impact of solar radiation and canopy structure on understory SIF; (3) normalized the OCO-2 SIF dataset at nadir, hotspot and darkspot viewing directions by using the FLiES model, and assessed the relationship between SIF and GPP; and (4) identified that SIF observed at the top of canopy was strongly influenced by understory reflectance and canopy structure. Results showed (1) the TOC SIF simulated by FLiES-SIF was closely correlated with SIF observations at a forest test site, and its performance was better than a 1-D model (Soil Canopy Observation, Photochemistry and Energy fluxes, SCOPE) and 3-D model (Discrete anisotropic radiative Transfer, DART); (2) the SIF emitted from understory contributed more than 51% to the total SIF in the wet season of a tropical savanna site, however, it only accounted for less than 10% of total SIF in an evergreen forest site; (3) SIF was most correlated with GPP in the hotspot direction, and the normalised SIF yield could better explain the variations of light use efficiency (LUE); (4) compared to canopy structure and leaf properties, the understory reflectance was the primary factor influencing the observed SIF at the top of the canopy. This thesis highlights the advantage of FLiES-SIF in capturing vegetation photosynthetic activities of ecosystems with complex canopy structures. This will significantly improve our understanding of vegetation responses to climate change, and this model can be implement for numerous related purposes.	en_AU
dc.format	Thesis (PhD)
dc.language.iso	en_US	en_AU
dc.relation	https://opus.lib.uts.edu.au/bitstream/10453/140431/2/02whole.pdf
dc.rights	info:eu-repo/semantics/openAccess
dc.rights	The author owns the copyright in this thesis including all reproduction and reuse rights for the work. The work may not be altered without the permission of the copyright owner. Attribution is essential when quoting or paraphrasing from this thesis.
dc.rights	au.edu.uts.lib/ppc
dc.title	Analyses of canopy photosynthesis derived from three-dimensional model simulations of sun-induced chlorophyll fluorescence	en_AU
dc.type	Thesis
utslib.copyright.status	open_access	*

Abstract:

Recently, measurements of sun-induced chlorophyll fluorescence (SIF) has become a new approach to estimate vegetation photosynthetic activity and detect vegetation stress. However, the environmental factors controlling SIF largely remain unknown for different vegetation biome types. In addition, SIF measured at the top of canopy (TOC) is confounded by interactions between solar radiation and vertical canopy structures. Hence, development of three-dimensional (3-D) radiative transfer models, capable of simulating SIF, would be of immense benefit to test and verify various hypothesises. The goal of this thesis is to develop a new 3-D SIF model and apply it to assess the relationship between SIF and plant photosynthetic activity across different spatial and temporal scales. Specifically, I (1) developed a new SIF module for FLiES (Forest Light Environmental Simulator) model (FLiES-SIF) and validated it with SIF observations at the seasonal scale; (2) partitioned SIF signals to overstory and understory layers by using FLiES-SIF, and then analysed the impact of solar radiation and canopy structure on understory SIF; (3) normalized the OCO-2 SIF dataset at nadir, hotspot and darkspot viewing directions by using the FLiES model, and assessed the relationship between SIF and GPP; and (4) identified that SIF observed at the top of canopy was strongly influenced by understory reflectance and canopy structure. Results showed (1) the TOC SIF simulated by FLiES-SIF was closely correlated with SIF observations at a forest test site, and its performance was better than a 1-D model (Soil Canopy Observation, Photochemistry and Energy fluxes, SCOPE) and 3-D model (Discrete anisotropic radiative Transfer, DART); (2) the SIF emitted from understory contributed more than 51% to the total SIF in the wet season of a tropical savanna site, however, it only accounted for less than 10% of total SIF in an evergreen forest site; (3) SIF was most correlated with GPP in the hotspot direction, and the normalised SIF yield could better explain the variations of light use efficiency (LUE); (4) compared to canopy structure and leaf properties, the understory reflectance was the primary factor influencing the observed SIF at the top of the canopy. This thesis highlights the advantage of FLiES-SIF in capturing vegetation photosynthetic activities of ecosystems with complex canopy structures. This will significantly improve our understanding of vegetation responses to climate change, and this model can be implement for numerous related purposes.

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