Effectiveness of photochemical reflectance index to trace vertical and seasonal chlorophyll a/b ratio in Haloxylon ammodendron

Abstract

Vegetation indices such as photochemical reflectance index (PRI) have been applied in tracing various biophysical and biochemical parameters within plants. However, less attention has been focused on chlorophyll (Chl) a/b ratio in arid environment. Quantitative estimation of Chl a/b ratio through remote sensing may provide important information regarding carbon balance and stress response in desert plants. We investigated the potential of PRI to trace Chl a/b ratio in Haloxylon ammodendron trees at Gurbantu ¨nggu ¨t Desert, China. The results revealed a seasonal and vertical variation in correlations. PRI was negatively correlated with Chl a/b ratio in all datasets, with pronounced sensitivity to changes in light across the canopy where low coefficient of determination (R 2 = 0.30) was obtained in bottom compared to the middle and top canopy assimilating branches. Seasonally, PRI-Chl a/b ratio relationship exhibited a higher R 2 for May-June dataset (R 2 = 0.62, P \ 0.001) and a lower RMSE of 0.18. A larger variability in both relationships was apparent when data from different heights were pooled together (total dataset). Although good correlation between seasonal PRI-Chl a/b relationship was found in top canopy branches, this relationship did not hold throughout the entire growing season. The identified normalized differential (ND) index (ND(510,570)) performed slightly better than the original PRI with R 2 improvement of 1 and 4 % for May-June and July-September datasets, respectively, and more than 5 % improvement in R 2 for within canopy datasets. In addition, both PRI and ND(510,570) performed poorly for pooled data. Therefore, within canopy variation and age-related changes must be considered when retrieving Chl a/b ratio through hyper-spectral remote sensing. Furthermore, both PRI and ND(510,570) must be applied with caution when dealing with desert species because of confounding factors related to strong erratic changes such as drought. Further studies on PRI mechanisms in different species under different environment are recommended.

Affecting Factors and Recent Improvements of the Photochemical Reflectance Index (PRI) for Remotely Sensing Foliar, Canopy and Ecosystemic Radiation-Use Efficiencies

“…PSII efficiency could not be efficiently tracked by PRI in varying light intensities, seasons and leaf colors due to the influence of chlorophyll, low temperature at night or low illumination on reflectance, which inhibit the epoxidation of the xanthophyllic cycle and retain more xanthophyllic pigments [87,113]. Likewise, the tracking of seasonal levels of Chlorophyll a/b (Chl a/b) using PRI was affected by high non-photochemical dissipation from the senescence of the vegetation and drought stress in desert species during growth [114]. PRI decreased throughout the soybean growing season due to elevated ozone concentrations, which increased the protective dissipation of excess energy and decreased the foliar contents of nitrogen and chlorophyll [115,116].…”

Spectral Reflectance Modeling by Wavelength Selection: Studying the Scope for Blueberry Physiological Breeding under Contrasting Water Supply and Heat Conditions

“…Independent of the plant species studied or the modeling methodology utilized for predicting chlorophyll concentration (Chl a, Chl b or Chl total), the coefficients of determination reported in the literature are usually high (R 2 Val > 0.65) [10,41,48,54,55], which is coincident with the results presented in this work. Interestingly, the higher R 2 Val values that were obtained for the estimation of Chl a/b values are also superior to those documented by other authors, which have been generated either via predictive models or through the study of SRIs [56]. The chlorophyll a and b ratio (Chl a/b) is a good indicator of stress in higher plants [57,58].…”

Physiological Study of the Efficacy of Archer® Eclipse in the Protection against Sunburn in Cucumber Plants

“…This could all suggest that non-treated plants suffered a greater stress intensity than the Archer ® Eclipse plants. The Chl a/b ratio, an indicator of environmental stress [25], was higher in treated than in non-treated plants, confirming that the treated plants suffered less stress. A decrease in this ratio indicates that the plants suffered a strong degree of oxidative stress and activated their antioxidant system to reduce ROS and turn part of Chl a into Chl b, as this is an O 2 consumption process which removes the aforementioned from the chloroplast.…”

“…The plants treated with Archer ® Eclipse had a higher total Chl concentration than the non-treated plants. The Chl content in leaves is one of the most important physiological characteristics that is altered under this type of stress, and it is considered one of the most important indicators of plants suffering sunburn [25].…”