Predicting Tissue Chloride Through FTIR-ATR Spectroscopy—Application of Exhaustive Feature Extraction Protocol

This study analyzed the relationships between tissue Cl and tissue light absorption in the wavelengths ranging from 399.9424 to 3997.363 (1746 spectra). The purpose was to determine plant tissue Cl concentrations non-destructively. Beauty leaf tree seedlings were grown in a glasshouse and were exposed to 0 and 75 mM NaCl for about 130 days. After harvest, the dried leaves were ground (< 1.0 mm) and scanned using FTIR. The leaf Cl concentration was determined chemometrically. Analysis of the spectra revealed the presence of clusters of wavenumbers, each wavelength displaying a different correlation with tissue chloride concentration. Application of exhaustive feature extraction technique enabled selection of 806 spectra (out of 1746) that correlated highly (r = 0.93) with the chemometrically determined Cl. These results clearly demonstrate that the tissue Cl can be estimated using FTIR spectra. The benefit of this technology is that large number of genotypes can be screened for salt tolerance, as the accumulation of Cl in the tissue indicate the degree of salt tolerance in many plant species. This technique can also be extended to other elemental analysis, thus saving the time and costs in plant nutrition and agronomic studies that involve selection of salt tolerant genotypes.