Hyperspectral Reflectance of Light-Adapted Leaves Can Predict Both Dark- and Light-Adapted Chl Fluorescence Parameters, and the Effects of Chronic Ozone Exposure on Date Palm (<i>Phoenix dactylifera</i>)

• Main Authors: Lorenzo Cotrozzi, Giacomo Lorenzini, Cristina Nali, Elisa Pellegrini, Vincenzo Saponaro, Yasutomo Hoshika, Leila Arab, Heinz Rennenberg, Elena Paoletti
• Format: Article
• Language: English
• Published: MDPI AG 2020-09-01
• Series: International Journal of Molecular Sciences
• Subjects: Fluorescence quenching; hyperspectral phenotyping; partial least squares regression; photosystem II activity; pulse-amplitude-modulation fluorometry; saturation pulse method
• Online Access: https://www.mdpi.com/1422-0067/21/17/6441

High-throughput and large-scale measurements of chlorophyll <i>a</i> fluorescence (ChlF) are of great interest to investigate the photosynthetic performance of plants in the field. Here, we tested the capability to rapidly, precisely, and simultaneously estimate the number of pulse-amplitude-modulation ChlF parameters commonly calculated from both dark- and light-adapted leaves (an operation which usually takes tens of minutes) from the reflectance of hyperspectral data collected on light-adapted leaves of date palm seedlings chronically exposed in a FACE facility to three ozone (O₃) concentrations (ambient air, AA; target 1.5 × AA O₃, named as moderate O₃, MO; target 2 × AA O₃, named as elevated O₃, EO) for 75 consecutive days. Leaf spectral measurements were paired with reference measurements of ChlF, and predictive spectral models were constructed using partial least squares regression. Most of the ChlF parameters were well predicted by spectroscopic models (average model goodness-of-fit for validation, <i>R²</i>: 0.53–0.82). Furthermore, comparing the full-range spectral profiles (i.e., 400–2400 nm), it was possible to distinguish with high accuracy (81% of success) plants exposed to the different O₃ concentrations, especially those exposed to EO from those exposed to MO and AA. This was possible even in the absence of visible foliar injury and using a moderately O₃-susceptible species like the date palm. The latter view is confirmed by the few variations of the ChlF parameters, that occurred only under EO. The results of the current study could be applied in several scientific fields, such as precision agriculture and plant phenotyping.