Solar-induced chlorophyll fluorescence (SIF) as a proxy of canopy photosynthesis for crops in the U.S. corn belt

Wu, Genghong

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https://hdl.handle.net/2142/117563 Copy

Description

Title

Solar-induced chlorophyll fluorescence (SIF) as a proxy of canopy photosynthesis for crops in the U.S. corn belt

Author(s)

Wu, Genghong

Issue Date

2022-11-28

Director of Research (if dissertation) or Advisor (if thesis)

Guan, Kaiyu

Doctoral Committee Chair(s)

Ainsworth, Elizabeth A.

Committee Member(s)

• Bernacchi, Carl J.
• Berry, Joseph A.

Department of Study

Natural Res & Env Sci

Discipline

Natural Res & Env Sciences

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Cropland
• gross primary production
• solar-induced chlorophyll fluorescence

Abstract

Quantifying canopy photosynthesis (gross primary production, GPP) and understanding its dynamics under climate change is crucial for accurate modeling of the global carbon cycle and food security. Recent advances in remotely sensed solar-induced chlorophyll fluorescence (SIF) have provided an exciting and promising opportunity for estimating GPP and understanding plant responses to stress. However, the linkage between SIF and GPP is complicated by instrumental, canopy structural, and leaf physiological factors, and how these factors affect canopy SIF and the resulting relationship with GPP is not well understood. An overarching question of this study is to investigate the performance of canopy far-red SIF as a proxy of GPP in crops (corn, soybean, and miscanthus) by utilizing long-term ground SIF and reflectance measurements concurrent with GPP at multiple site-years in the U.S. Corn Belt. Chapters 2 and 3 analyzed the instrumental effects on canopy SIF and SIF-GPP relationships. I found that Fraunhofer line depth (FLD)-based methods were less sensitive to the temperature of the enclosure where the spectral system was located, and upscaling nadir SIF to GPP footprint had no effect on the SIF-GPP relationship due to the relatively homogeneous conditions in croplands. Chapters 4 and 5 investigated the effects of structural and physiological factors on the canopy SIF-GPP relationships in the three species. Canopy SIF reached its seasonal maximum 14–17 days earlier than GPP in soybean, which can be explained by a divergence in the seasonality between absorbed photosynthetic active radiation (APAR) and canopy chlorophyll content (ChlCanopy). Different SIF-GPP relationships were found in corn and miscanthus, which were mainly caused by physiological factors. A large decline of fluorescence yield (ΦF) under high light, temperature, and water vapor deficit (VPD) conditions led to a SIF midday depression and weakened the SIF-GPP relationship in miscanthus. Chapter 6 explored the capability of canopy SIF to track the ozone stress on soybean and found that SIF captured the elevated ozone effect on soybean, including the damage to canopy structure and acceleration of senescence. Except for SIF, chapter 7 tested the performance of a new proxy, radiance-based NIRv (NIRv,Rad), in sub-daily to daily GPP estimation in corn and soybean. Overall, NIRv,Rad outperformed SIF and explained ~80% of the variation of half-hourly corn and soybean GPP. This thesis advances our mechanistic understanding of the canopy SIF signal and its linkage with GPP in crops and contributes to improving crop GPP estimation at fine temporal scales.

Graduation Semester

2022-12

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Genghong Wu

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