Spectral reflectance and leaf internal structure changes of barley plants due to phytoextraction of zinc and cadmium

The focus of our research is to seek spectral signatures that indicate the impact and content of heavy metals in the leaves and canopies of living plants during the process of phytoremediation. Potted plants of barley (Hordeum vulgare) were grown for 5-6 weeks before being subjected to metal treatments of Zn and Cd. Diffuse reflectance spectra (350-2500 nm) of the plant canopies were collected daily using a portable spectroradiometer throughout the treatment period. Foliar structural changes of Zn-treated plants included a decrease in intercellular space, palisade and epidermal cell size while Cd-treated plants displayed fewer structural changes in leaf. Spectral analysis revealed that the band ratios at 1110 nm to that at 810 nm might be used as an indicator of the accumulation of certain metals in plant shoots. Normalized Difference Vegetation Index (NDVI) and leaf-water-content indices examined as part of our spectral analysis were not able to distinguish plants treated with different metals. Our ratio index R1110/R810, on the other hand, correlates closely with the magnitude of leaf structural changes. This study suggests that the infrared reflectance spectrum (800-1300 nm) of plant canopy might provide a non-intrusive monitoring method for the physiological status of plants grown on heavy metal contaminated soil.