Abstract:

It is of significant importance for using leaf spectral reflectance characteristics to estimate leaf chlorophyll fluorescence parameters in crop plants. We carried out two filed experiments in Nanjing to investigate the relationships between chlorophyll fluorescence parameters and spectral reflectance characteristics in top four leaves under different nitrogen levels in wheat (Triticum aestivum L.) cultivars Ningmai 9 (low protein content), Huaimai 20 (medium protein content), and Yumai 34 (high protein content). Experiment one was conducted with Ningmai 9 and Huaimai 20 and five nitrogen application levels of 0, 75, 150, 225, and 300 kg ha^-1 in 2003 to 2004. Experiment two was designed for Ningmai 9 and Yumai 34 with three nitrogen application levels of 0, 90, and 270 kg ha^-1 in 2004 to 2005. The dynamic change patterns and interrelationships between chlorophyll fluorescence parameters and spectral reflectance in top four leaves of wheat cultivars under different nitrogen levels in two years were analyzed. The results indicated that the leaf chlorophyll fluorescence parameters F_v/F_m and F_v/F_o in wheat increased with increasing nitrogen rates, whereas the leaf spectral reflectance varied distinctly with nitrogen rates, leaf positions and growth process. The correlations between chlorophyll fluorescence parameters and spectral reflectance in the top 1st and 2nd leaves were stabilized in the ranges of visible light (520–680nm) and near infrared light (750–850nm). The leaf reflectance spectral indices DVI (750, 550), DVI (735, 690) and TVI (750, 670, 550) were all highly correlated with the leaf chlorophyll fluorescence parameters F_o, F_m, F_v, F_v/F_m, F_v/F_o, F_s, F_m’, F_o’, F_v’, and F_v’/F_m’ in top 2 leaves, and the DVI (750, 550) had the best correlation. In addition, there were no obvious differences on regression coefficients among different cultivars and growth stages. These results suggested that it is feasible to monitor leaf chlorophyll fluorescence parameters by leaf reflectance spectra in wheat.

Key words: Wheat (Triticum aestivum L.), Leaf position, Fluorescence parameter, Reflectance spectra, Vegetation index