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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 groundbased 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.

The influence of the environmental stress factors, salinity and enhanced UV-B radiation, on young nitrogen fixing soybean plants (Glycine max L.) was investigated by using hyperspectral reflectance data. Soybean is the leading oilseed crop produced and consumed worldwide. The soybean plants were grown in a growth clamber as water cultures on Helrigel nutrient solution. Three day's seedlings were inoculated with suspension of Bradyrhizobium japonicum strain 273. Salinity was performed at growth stage of 2 nd -4 th expanded leaves by adding of NaCl in the nutrient solution in concentrations 40 mM and 80 mM. Plants were divided into six groups. The first three groups consisted of untreated (control) and treated only with two NaCl concentrations plants. The other three groups (control and salinized) on the 14 th day after the treatment were illuminated for four hours with UV-B radiation at intensity 64.4 μmol m -2 s -1 . Spectral reflectance was registered by a portable fiber-optic spectrometer in the visible and near infrared (NIR) spectral ranges (450-850 nm). Data were subjected to statistical analysis through the Student's t-criterion in four spectral ranges: green, red, red-edge and NIR (520-580 nm; 640-680 nm; 690-720 nm; 720-780 nm). The results from spectral reflectance and biochemical analysis (evaluated stress markers) revealed that both treatments (salinity and salinity + UV-B radiation) bring the plants to stress and to decline of the biological nitrogen fixation. The UV-B treatment decreases the salinity action and partly restores the physiological state of the plants.

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Abstract. Hyperspectral remote sensing provides for significant advancement in the evaluation of the subtle changes in biophysical and biochemical attributes of the crop plants. Accurate estimates of leaf pigments, nitrogen, dry matter, water content, and leaf area index (LAI) from remotely sensed data can assist in determining the vegetation physiological state. In this paper, hyperspectral remote sensing measurements of the leaf reflectance were applied for assessing the effect of biotic stress (viral infection) on the spectral behaviour and biophysical variables of young potato plants, cultivar Agata, infected with Potato Virus Y (PVY). Spectral reflectance data were collected by means of a portable fiber-optics spectrometer in the visible and near infrared spectral ranges (350-1100 nm) with a spectral resolution of 1.5 nm. For the assessment of differences between the reflectance data of healthy and infected plant data processing techniques, such as Student's t-test, first derivative analyses, and estimation of vegetation indices, were applied. The analyses were performed in green, red, red edge and near infrared spectral ranges (450-850 nm) where the differences were the most significant and give information about changes in the chlorophyll and pigment content, moisture content, cells structures, and plant stress. Several vegetation indices (NDVI -Normalized Difference Vegetation Index, fD -Disease Index, SR -Simple Ratio, TCARI -Transformed Chlorophyll Absorption Reflectance Index, etc.) were computed and the best results for assessing the changes in the physiological state of the plants gave TCARI. A strong relationship was found between the results of the spectral analyses and the serological test DAS-ELISA was applied to assess the presence and the degree of the PVY infection.