**5.1 Leaf spectral reflectance**

Hyperspectral reflectance data were collected in VIS and NIR spectral ranges (450-850 nm) by using a portable fibre-optics spectrometer USB2000 (http://www.OceanOptics.com). In the range investigated the main part of the reflected from leaves radiation is concentrated. Data were obtained at 1170 spectral bands with a step of 0.3 nm and a spectral resolution of 1.5 nm.

The reflectance measurements were carried out on an experimental setup in laboratory (Fig. 10). The entrance lens, a standard screen WS1 (diffuse reflectance white plastic with Lambertian reference surface) and plant leaves were set on a special adjustable platform, which provides an accurate relative positioning of all equipment components. The fibreoptic cable was located at nadir view (perpendicular to leaf surface). As a light source a halogen lamp providing homogeneous illumination of measured leaf surfaces was used. The acquisition and processing of data were carried out by means of portable computer using specialized software. The spectral reflectance characteristics were obtained as a ratio of the reflected radiation from the leaves and the reflected radiation from WS1 screen. The measurements were performed on fresh, immediately picked off soybean leaves at the stage of 4th trifoliate expanded leaf from up to 25 plants from each investigated group.

Fig. 10. Experimental setup for spectral reflectance measurements.

Spectral Remote Sensing of the Responses of Soybean Plants to Environmental Stresses 231

600 650 700 750 800 850 900 Wavelength, nm

4 =736nm 5 =755nm

1 =678nm

Fig. 11. Characteristic wavelengths chosen for statistical analysis of fluorescence.

2 =694nm 3 =712nm

All statistical analyses were conducted using the STATISTICA software, Version 6.1, 2002,

The effect of salinity on leaf spectral reflectance of soybean plants for the first part of the experiments (see Fig. 3) is shown in Fig. 12 (Krezhova et al., 2009a). The SRC were averaged over all studied areas (pixels) of leaves of control and treated with each of the two salt concentrations plants. The discrepancy (lack of coincidence or very small differences) between the characteristics of control and treated by 40 mM NaCl plants was observed in

At 80 mM NaCl the values of the average SRC of treated leaves with respect to control decrease significantly in both the green and red (640-680 nm) ranges. In the red edge (680- 720 nm) it is observed a shift to longer wavelengths (8 nm) indicating the occurrence of stress. Necrosis spots were seen on some of the leaves of plants treated with this NaCl concentration (Fig. 3 c). The red edge position changed significantly with the increase in NaCl concentration applied to the plants and it is a consequence of the decreased chlorophyll content determined by biochemical method. In the NIR range the reflectance

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**6.1 Influence of a single stress factor at soybean plants** 

the green (520-580 nm, maximal chlorophyll reflection) and NIR ranges.

(http://www.statsoft.com).

**6. Results and discussion** 

changed non-significant against the control.

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Relative emission intensity

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1.0
