A pilot study on the effect of Cu, Zn, and Cd on the spectral curves and chlorophyll of wheat canopy at tiller stage

The aim of this study was to investigate canopy spectral reflectance responses to
different levels of heavy metals copper (Cu), zinc (Zn), and cadmium (Cd) induced
stress. Random blocks design experiment was conducted to simulate Cu, Zn, and Cd
at five concentration levels. Chlorophyll and visible and near infrared canopy
reflectance were measured for each treatment 56 days after seeding using chlorophyll
meter SPAD-502 and spectroradiometer, respectively. New vegetative indices termed
ratio of inclination angles (RIA), MERIS (the medium resolution imaging spectrometer)
terrestrial chlorophyll index (MTCI), and normalized difference vegetation index
(NDVI) were used to assess the response of canopy spectral reflectance to different
heavy metal levels. Significant spectral variability especially in blue, red, and near
infrared reflectance was observed for different heavy metal treatments. One-sample
test showed significant difference for NDVI, MTCI, and RIA among five-level
treatments at the 0.01 level. Correlation analysis demonstrated that the two
vegetative indices (RIA and MTCI) were significantly correlated with chlorophyll
meter values for Cd, Cu, and Zn treatments. However, NDVI was only significantly
correlated with chlorophyll meter values for Cu and Zn treatments. Linear regression
analysis also illustrated that RIA and MTCI were potential indices for predicting
chlorophyll concentration with significant F test under Cu-, Zn-, and Cd-mediated
stress.