A retrieval algorithm to evaluate the Photosystem I and Photosystem II spectral contributions to leaf chlorophyll fluorescence at physiological temperatures

Abstract

A new computational procedure to resolve the contribution of Photosystem I (PSI) and Photosystem II (PSII) to the leaf chlorophyll fluorescence emission spectra at room temperature has been developed. It is based on the Principal Component Analysis (PCA) of the leaf fluorescence emission spectra measured during the OI photochemical phase of fluorescence induction kinetics. During this phase, we can assume that only two spectral components are present, one of which is constant (PSI) and the other variable in intensity (PSII). Application of the PCA method to the measured fluorescence emission spectra of Ficus benjamina L. evidences that the temporal variation in the spectra can be ascribed to a single spectral component (the first principal component extracted by PCA), which can be considered to be a good approximation of the PSII fluorescence emission spectrum. The PSI fluorescence emission spectrum was deduced by difference between measured spectra and the first principal component. A single-band spectrum for the PSI fluorescence emission, peaked at about 735 nm, and a 2-band spectrum with maxima at 685 and 740 nm for the PSII were obtained. A linear combination of only these two spectral shapes produced a good fit for any measured emission spectrum of the leaf under investigation and can be used to obtain the fluorescence emission contributions of photosystems under different conditions. With the use of our approach, the dynamics of energy distribution between the two photosystems, such as state transition, can be monitored in vivo, directly at physiological temperatures. Separation of the PSI and PSII emission components can improve the understanding of the fluorescence signal changes induced by environmental factors or stress conditions on plants.

Disentangling Changes in the Spectral Shape of Chlorophyll Fluorescence: Implications for Remote Sensing of Photosynthesis

“…The spectral shape associated with changes in NPQ shows a similar pattern to Farooq et al () and Lambrev et al (), suggesting that the change at F t,720 is the result of rapidly reversible energy‐dependent quenching, whereas the decrease at F t,680 is induced by both PsbS‐independent mechanisms and energy‐dependent quenching. Further, the decrease in F t,680 under increasing light has been noted in other works and attributed to changes in PSII compared to PSI fluorescence (Nematov et al, ), since PSI fluorescence is thought to be negligible <680 nm and not modified by changes in NPQ/PQ (Franck et al, ; Palombi et al, ; Figures S7 and S8). Indeed, our canopy results show a decrease in red:far‐red SIF with increasing light and changes in LUE (Figures and S12); however, even under highly stressed conditions (Figure ), the leaf level change in red:far‐red ChlF is only 15%, which would require a significant improvement in SIF retrievals (which currently have systematic errors of the same or greater magnitude) to utilize red:far‐red SIF to assess NPQ dynamics.…”

“…The magnitude and spectral shape of leaf ChlF are known to change with irradiance conditions (Pinto et al, ), chlorophyll concentration (Buschmann, ; Gitelson et al, ; Hak et al, ; Lichtenthaler et al, ), physiological condition (PSI/PSII contributions, NPQ; Franck et al, , ; Lambrev et al, ; Palombi et al, ; Rizzo et al, ), temperature (Agati, ; Croce et al, ), photosystem stoichiometry and structure (Farooq et al, ; Johnson et al, ), and leaf optical properties (Gitelson et al, ; Vilfan et al, ). At steady state, a large body of research suggests that deviations in the red (~685 nm) to far‐red (~750 nm) ChlF ratio are controlled by Chl concentration, which regulates the degree of reabsorption in the red part of the spectrum along the escape path of the photon (Buschmann, ; Gitelson et al, ; Lichtenthaler et al, ).…”

Model-based analysis of the relationship between sun-induced chlorophyll fluorescence and gross primary production for remote sensing applications

“…The contribution of PSII to total fluorescence emission is greater in the red than in the far-red, while PSI emission spectrum shows a peak in the far-red (Franck et al, 2002). However, the dynamics of chlorophyll fluorescence are usually associated with PSII photochemistry because the contribution of fluorescence from PSI is generally low to total signal and remains constant under illumination (Genty et al, 1990;Palombi et al, 2011).…”

Gross Primary Production of a Wheat Canopy Relates Stronger to Far Red Than to Red Solar-Induced Chlorophyll Fluorescence

“…Compared to far red fluorescence, red fluorescence-produced dominantly by photosystem II (PSII)-is the most variable part of ChlF [30]. Hence, RSIF would be a preferential choice to assess physiologically-induced ChlF variations, and the detection of both peaks would provide complementary information on photosystem I (PSI) and PSII emissions [31]. In this study, we used the field platform for continuous measurements of fluorescence [32] located in Avignon, France to investigate both diurnal and seasonal dynamics of RSIF and FRSIF over a wheat crop during a complete vegetative cycle.…”