Exploring the potential of leaf reflectance spectra for retrieving the leaf maximum carboxylation rate

Abstract

ABSTRACTThe maximum carboxylation rate (Vcmax) is a key photosynthetic parameter that is determined by the leaf biochemistry and environmental conditions. Numerous studies have shown that plant biochemical, physiological and structural parameters can be estimated from reflectance spectra. Therefore, it is reasonable to assume that Vcmax can be spectrally determined. Here, we investigate the potential of leaf reflectance spectra for retrieving the maximum carboxylation rate of leaves. Measurements of leaf reflectance, carbon dioxide (CO2) response curves, leaf chlorophyll-a + b (chl-a + b) etc., were made on 80 crop, shrub and tree leaves. Then, the leaf Vcmax,25 was linked to leaf biochemistry and spectral reflectance. A reliable relationship, with a coefficient of determination (R2) value of 0.75, was found between the leaf chl-a + b content and Vcmax,25. The leaf Vcmax,25 values were also significantly correlated with chl-a + b-sensitive spectral indices with the highest R2 value that was found being 0.83 for the ratio spectral index (RSI) using reflectances at 1089 nm and 695 nm. Finally, multiple stepwise regression (MSR) and a partial least-squares regression (PLSR) modelling approach were used to estimate Vcmax,25 from leaf reflectances. The results confirmed that Vcmax,25 can be reliably estimated from leaf reflectance spectra and give an R2 value >0.80. These findings show that leaf chl-a + b can be used as a proxy for leaf Vcmax,25 and that leaf Vcmax,25 can be spectrally determined using leaf reflectance data.