A physiological signal derived from sun-induced chlorophyll fluorescence quantifies crop physiological response to environmental stresses in the U.S. Corn Belt

Authors: KIMM, HYUNGSUK - University Of Illinois; GUAN, KAIYU - University Of Illinois; JIANG, CHONGYA - University Of Illinois; MIAO, GUOFANG - University Of Illinois; WU, GENGHONG - University Of Illinois; SUYKER, ANDREW - University Of Nebraska; Ainsworth, Elizabeth - Lisa; Bernacchi, Carl; Montes, Christopher; BERRY, JOSEPH - Carnegie Institute - Stanford; YANG, XI - California Institute Of Technology; FRANKENBERG, CHRISTIAN - California Institute Of Technology; CHEN, MIN - University Of Wisconsin; KOEHLER, PHILIPP - California Institute Of Technology

Submitted to: Environmental Research Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/18/2021
Publication Date: 12/6/2021
Citation: Kimm, H., Guan, K., Jiang, C., Miao, G., Wu, G., Suyker, A.E., Ainsworth, E.A., Bernacchi, C.J., Montes, C.M., Berry, J.A., Yang, X., Frankenberg, C., Chen, M., Koehler, P. 2021. A physiological signal derived from sun-induced chlorophyll fluorescence quantifies crop physiological response to environmental stresses in the U.S. Corn Belt. Environmental Research Letters. 16. Article 124051. https://doi.org/10.1088/1748-9326/ac3b16.
DOI: https://doi.org/10.1088/1748-9326/ac3b16

Interpretive Summary: Plant absorb light, which provides the energy for photosynthesis that allows for plant growth. But plants will emit some of this light from leaves in a process called chlorophyll fluorescence. At a canopy scale, this is referred to as sun-induces chlorophyll fluorescence, which is abbreviated as SIF. SIF has been shown to be linked with canopy photosynthetic rates, which is very useful because measuring canopy photosynthesis is a traditionally difficult task. But what really controls SIF is more than the photosynthesis of the plant canopy as it is also impacted by how the leaves and branches in a canopy are arranged as well as how much sunlight is available. This study links the physiology of plants with SIF to try to understand how stresses, such as high temperature and dryer conditions, impact the SIF signal. The results show that most of the SIF signal measured is driven by the canopy arrangement, with only 15-30% of the SIF signal being determined by photosynthesis. Under stress, this study showed that the signal impacted by photosynthesis increased whereas the structural signals did not change. These results show that SIF is a useful tool to understand plant photosynthesis and the tool becomes better when trying to assess plant responses to harsher growth conditions.

Technical Abstract: Sun-induced chlorophyll fluorescence (SIF) measurements have shown unique potential for quantifying plant physiological stress. However, recent investigations found canopy structure and radiation largely control SIF, and physiological relevance of SIF remains yet to be fully understood. This study aims to evaluate whether the SIF-derived physiological signal improves quantification of crop responses to environmental stresses, by analyzing data at three different spatial scales within the U.S. Corn Belt, i.e., experiment plot, field, and regional scales, where ground-based portable, stationary and space-borne hyperspectral sensing systems are used, respectively. We found that, when controlling for variations in incoming radiation and canopy structure, crop SIF signals can be decomposed into structural (64~82%) and physiological information (i.e., physiological SIF yield, FF, 17~31%), which confirms the contribution of physiological variation to SIF. We further evaluated whether FF indicated plant responses under high-temperature and high vapor pressure deficit (VPD) stresses. The plot-scale data showed that FF responded to the proxy for physiological stress (partial correlation coefficient, rp=0.40, p<0.001) while structural signals of SIF did not respond (p>0.1). The field-scale FF data showed water deficit stress from the comparison between irrigated and rainfed fields, and FF was positively correlated with canopy-scale stomatal conductance, a reliable indicator of plant physiological condition (correlation coefficient r=0.60 and 0.56 for an irrigated and rainfed sites, respectively). The regional-scale data showed, for the U.S. Corn Belt, FF was more strongly correlated spatially with air temperature and VPD (r=0.23 and 0.39) than SIF (r=0.11 and 0.34). The lines of evidence suggested that FF reflects crop physiological responses to environmental stresses with greater sensitivity to stress factors than SIF, and the stress quantification capability of FF is spatially scalable. Utilizing FF for physiological investigations will contribute to improving our understanding of vegetation responses to high-temperature and high-VPD stresses.