Exploring the Sensitivity of Solar-Induced Chlorophyll Fluorescence at Different Wavelengths in Response to Drought

Abstract

Due to the mechanistic coupling between solar-induced chlorophyll fluorescence (SIF) and photosynthesis, SIF has an advantage over greenness-based vegetation indices in detecting drought. Since photosystem I (PSI) contributes very little to red SIF, red SIF is assumed to be more responsive to environmental stress than far-red SIF. However, in addition to affecting photosynthesis, drought also has an impact on vegetation chlorophyll concentration and thus affects the reabsorption process of red SIF. When these responses are entangled, the sensitivity of SIF in the red and far-red regions in response to drought is not yet clear. In this study, we conducted a water stress experiment on maize in the field and measured the upward and downward leaf SIF spectra by a spectrometer assembled with a leaf clip. Simultaneously, leaf-level active fluorescence was measured with a pulse-amplified modulation (PAM) fluorometer. We found that SIF, after normalization by photosynthetically active radiation (PAR) and dark-adapted minimal fluorescence (Fo), is a better estimation of SIF yield. By comparing the wavelength-dependent link between SIF yield and nonphotochemical quenching (NPQ) across the range of 660 to 800 nm, the results show that red SIF and far-red SIF have different sensitivities in response to drought. SIF yield in the far-red region has a strong and stable correlation with NPQ. Drought not only reduces red SIF due to photosynthetic regulation, but it also increases red SIF by reducing chlorophyll content (weakening the reabsorption effect). The co-existence of these two contradictory effects makes the red SIF of leaf level unable to reliably indicate NPQ. In addition, the red:far-red ratio of downward SIF and the ratio between the downward SIF and upward SIF at the red peak can be good indicators of chlorophyll content. These findings can help to interpret SIF variations in remote sensing techniques and fully exploit SIF information in red and far-red regions when monitoring plant water stress.

Modeling of Cotton Yield Estimation Based on Canopy Sun-Induced Chlorophyll Fluorescence

“…This method can extract a more accurate and reliable SIF data set from long-term field observations for studying the relationship between SIF and vegetation photosynthesis [73]. SIF can better estimate yield after PAR normalization [74,75].…”

Optimized Transfer Learning for Chlorophyll Content Estimations across Datasets of Different Species Using Sun-Induced Chlorophyll Fluorescence and Reflectance

“…The attenuated peak around 680 nm in the SIFY spectra of rapeseed might be attributed to the thicker and more complex leaf structure of rapeseed leaves, resulting in a more pronounced reabsorption effect for SIF before 700 nm [34]. Moreover, both the rice and rapeseed datasets exhibited clear dual peaks, indicating that the samples used in all four datasets were grown under relatively normal nutrient and moisture levels [25,35], thereby avoiding changes in SIF signal characteristics due to environmental stress. The observed reflectance spectra showed variations across spectral bands associated with C ab (450-750 nm), mesophyll structure (800-1250 nm), water absorption (1300-2400 nm), and dry matter content (1600-2500 nm) [36].…”

The Afternoon/Morning Ratio of Tower-Based Solar-Induced Chlorophyll Fluorescence Can Be Used to Monitor Drought in a Chinese Cork Oak Plantation

“…However, because red SIF is affected by the chlorophyll reabsorption effect, the reduction in chlorophyll content caused by drought leads to the decrease in red SIF emission on the one hand, and an increase in red SIF due to the reduction in the reabsorption effect on the other hand [55]. These two simultaneous and contradictory effects limit the precision of red SIF for drought monitoring.…”