Assessment of the effect of salinity on the early growth stage of soybean plants (Glycine max L.)

The effects of different salt concentration treatment of soybean plants and the occurrence of salinity stress have been assessed from a comparative analysis of remotely sensed ground-based spectral reflectance data and biochemical parameters. The contents of phenols, proline, malondialdehid, hydrogen peroxide, thiol groups, and chlorophyll a and b have been determined. The soybean plants were grown under controlled conditions as water cultures on Helrigel nutrient solution. Salinity was performed at the stage of 2^nd to 4^th trifoliate expanded leaves by adding of NaCl in the nutrient solution in concentrations 40 mM and 80 mM. The leaf spectral reflectance was measured in laboratory in the visible and near infrared spectral ranges using a fibre-optic multichannel spectrometer. An algorithm based on multivariate statistical analysis of the leaf reflectance spectra was developed. It includes Student´s t-criterion, discriminant analysis and derivative analysis. The spectral intervals of interest were the green, red, red-edge and near infrared ranges of the spectrum. Statistically significant differences at p<0.05 were found between the leaf spectral reflectance data of control and treated plants at 80 mM NaCl in all of the ranges examined with the exception of the near infrared range. No statistically significant differences were established at 40 mM NaCl treatment. Some of the biochemical parameters (proline, malondialdehid, thiol groups) were found at salinity treatment by 40 mM NaCl to increase in value more than 10% while the chlorophyll a and b concentrations decreased more than 20%. This trend was preserved for the 80 mM NaCl treatment as the corresponding parameters changed by about 45% on average, which is symptomatic for the stressed plants.