Impact of Structural, Photochemical and Instrumental Effects on Leaf and Canopy Reflectance Variability in the 500–600 nm Range

Adrián Moncholi-Estornell,Zbyněk Malenovský,Shari Van Wittenberghe,Luis Alonso,Maria Pilar Cendrero-Mateo,José Moreno

doi:10.3390/rs14010056

Abstract

Current rapid technological improvement in optical radiometric instrumentation provides an opportunity to develop innovative measurements protocols where the remote quantification of the plant physiological status can be determined with higher accuracy. In this study, the leaf and canopy reflectance variability in the PRI spectral region (i.e., 500–600 nm) is quantified using different laboratory protocols that consider both instrumental and experimental set-up aspects, as well as canopy structural effects and vegetation photoprotection dynamics. First, we studied how an incorrect characterization of the at-target incoming radiance translated into an erroneous vegetation reflectance spectrum and consequently in an incorrect quantification of reflectance indices such as PRI. The erroneous characterization of the at-target incoming radiance translated into a 2% overestimation and a 31% underestimation of estimated chlorophyll content and PRI-related vegetation indexes, respectively. Second, we investigated the dynamic xanthophyll pool and intrinsic Chl vs. Car long-term pool changes affecting the entire 500–600 nm spectral region. Consistent spectral behaviors were observed for leaf and canopy experiments. Sun-adapted plants showed a larger optical change in the PRI range and a higher capacity for photoprotection during the light transient time when compared to shade-adapted plants. Outcomes of this work highlight the importance of well-established spectroscopy sampling protocols to detect the subtle photochemical features which need to be disentangled from the structural and biological effects.

Highlights

Introduction published maps and institutional affilPlant photosynthesis is a key carbon sink process of the Earth’s terrestrial carbon cycle, which is strongly controlled by abiotic factors including water, nutrients and light availability
We studied in detail the incorrect characterization of the at-target incident radiance, as well as the photochemical reflectance index (PRI) dynamics triggered by quick xanthophyll pool variations and/or Chl vs. Car long-term pool changes on beech saplings grown under three different light conditions: full shade, sun exposure and intermediate sun and shade exposure
85% of samples presented a negative difference value, indicating that the light arriving at HW is higher than the light reaching TW

Summary

Introduction

Introduction published maps and institutional affilPlant photosynthesis is a key carbon sink process of the Earth’s terrestrial carbon cycle, which is strongly controlled by abiotic factors including water, nutrients and light availability. Current novel spectroradiometers with a high spectral resolution allow for enhanced retrieval of plant biophysical parameters, such as canopy water content [2], nitrogen content [3], pigment composition [4], chlorophyll (Chl) fluorescence [5,6,7,8], or proxies for the light use efficiency of vegetation at multiple spatial scales [9]. The latter two are strongly driven by the amount of absorbed photosynthetic active radiation (APAR, 400–700 nm), i.e., the energy fueling the plant photosynthesis mechanisms inside leaves. De-excitation of the APAR energy, received by the photosynthetic antenna, takes place under steady-state conditions through three iations.

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Discussion

Conclusion