Nonlinear Relationship Between the Yield of Solar-Induced Chlorophyll Fluorescence and Photosynthetic Efficiency in Senescent Crops

Leizhen Liu,Xinyi Han,Jianhua Yang,Wenhui Zhao,Qiu Shen,Jianjun Wu,Feng Tian,Yanguo Teng

doi:10.3390/rs12091518

Abstract

It has been demonstrated that solar-induced chlorophyll fluorescence (SIF) is linearly related to the primary production of photosynthesis (GPP) in various ecosystems. However, it is unknown whether such linear relationships have been established in senescent crops. SIF and GPP can be expressed as the products of absorbed photosynthetically active radiation (APAR) with the SIF yield and photosystem II (PSII) operating efficiency, respectively. Thus, the relationship between SIF and GPP can be represented by the relationship between the SIF yield and PSII operating efficiency when the APAR has the same value. Therefore, we analyzed the relationship between the SIF yield and the PSII operating efficiency to address the abovementioned question. Here, diurnal measurements of the canopy SIF (760 nm, F760) of soybean and sweet potato were manually measured and used to calculate the SIF yield. The PSII operating efficiency was calculated from measurements of the chlorophyll fluorescence at the leaf level using the FluorImager chlorophyll fluorescence imaging system. Meanwhile, field measurements of the gas exchange and other physiological parameters were also performed using commercial-grade devices. The results showed that the SIF yield was not linearly related to the PSII operating efficiency at the diurnal scale, reflecting the nonlinear relationship between SIF and GPP. This nonlinear relationship mainly resulted from the heterogeneity and diurnal dynamics of the PSII operating efficiency and from the intrinsic diurnal changes in the maximum efficiency of the PSII photochemistry and the proportion of opened PSII centers. Intensifying respiration was another factor that complicated the response of photosynthesis to the variation in environmental conditions and negatively impacted the relationship between the SIF yield and the PSII operating efficiency. The nonlinear relationship between the SIF yield and PSII efficiency might yield errors in the estimation of GPP using the SIF measurements of senescent crops.

Highlights

Solar-induced chlorophyll fluorescence (SIF) is emitted at 650–850 nm by leaf pigments when absorbed photosynthetically active radiation (APAR) in the 400–700 nm range cannot be fully used for photosynthesis
We aimed to address the following questions: (1) Does SIF show a linear relationship with gross primary production of photosynthesis (GPP) in senescent crops? (2) If the relationship is nonlinear, what caused the result? Answers to these questions can provide a further understanding of the application of SIF in the large-scale detection of GPP
Our study explored the diurnal patterns of SIF accompanied by photosynthesis and revealed their relationship in senescent crops

Summary

Introduction

Solar-induced chlorophyll fluorescence (SIF) is emitted at 650–850 nm by leaf pigments (i.e., chlorophyll a) when absorbed photosynthetically active radiation (APAR) in the 400–700 nm range cannot be fully used for photosynthesis. SIF has shown a strong link with photosynthesis because it competes with two other fates of absorbed photons in the pigment bed (i.e., photochemistry and heat dissipation) for the same excitation energy [1]. A linear relationship between SIF and GPP was successfully found based on the measurements of spaceborne, airborne, and continuous ground-based conditions [11,15,16]. Such empirical linear relationships of SIF have been successfully used to directly estimate the GPP

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