Asymmetry of leaf internal structure affects PLSR modelling of anatomical traits using VIS-NIR leaf level spectra

ABSTRACT

Leaf traits can be used to elucidate vegetation functional responses to global climate change. Pigments, water and leaf mass per area are the most used traits. However, detailed anatomical traits such as leaf thickness, the thickness of palisade and spongy parenchyma are often neglected, although they affect leaf physiological function and optical properties. Our aim was to produce partial least squares regression (PLSR) models for estimating leaf traits using biconical reflectance factor (BCRF). We established that estimation of leaf anatomical properties differs when using BCRF obtained from the upper and lower surface of the leaf. PLSR explained that 90% of the variability was based on total chlorophyll content (R² = 0.95), spongy parenchyma to leaf thickness ratio (R² = 0.94), equivalent water thickness (R² = 0.93) and leaf mass per area (R² = 0.91) or leaf thickness (R² = 0.90). We conclude that internal asymmetry in leaf structure affects significantly leaf optical properties and should not be neglected in radiative transfer modelling at the leaf level and when upscaling leaf properties to the canopy.

KEYWORDS:

• Planar leaves
• leaf thickness
• palisade
• spongy parenchyma
• contact probe
• two-sided reflectance
• leaf optical properties
• leaf traits
• vegetation function

Acknowledgments

The study was funded by the Ministry of Education, Youth and Sports of the Czech Republic, scheme INTER-EXCELLENCE, project No. LTAUSA18154. The contribution of Petya Campbell was supported by NASA grants NNH17ZDA001N and 80NSSC24K0044. Lucie Červená was partly supported in the phase of writing by Charles University UNCE/HUM 018. We thank to Miroslav Barták (CUNI) for graphical technical help, Drahomíra Bartáková and Zdeňka Češpírová (CUNI) for help with leaf hand sectioning and cross section analyses.

Disclosure statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Data availability statement

The data presented in this study are available on reasonable request from the corresponding author.

Additional information

Funding

The work was supported by the Ministry of Education Youth and Sports [INTER-EXCELLENCE, LTAUSA18154]; by the National Aeronautics and Space Administration [NNH17ZDA001N; 80NSSC24K0044]; and by Charles University [UNCE/HUM 018].