Dora D. Krezhova

Early detection of changes in leaf reflectance of pea plants (Pisum sativum L.) under herbicide action

Based on high resolution leaf spectral reflectance data a new technique was developed and applied to detect damages of agricultural plants under the action of low intensity stress factors (herbicides) which at very low concentrations could not be established by the standard biochemical and biometric techniques. Results are presented from a remote sensing study of the peculiarities of the leaf spectral reflectance of pea plants (Pisum salivum L.) treated with atrazine and 2.4-D (2.4 - phenoxyacetic acid) at three low concentrations (0.01 /spl mu/M, 0.1 /spl mu/M and 1 /spl mu/M, respectively 2.15, 21.5, and 215 /spl mu/g/l for atrazine and 2.59, 25.9, and 259 /spl mu/g/l for 2.4-D) as compared to the field dose of these herbicides commonly used in the agricultural practice. The physiological status of the plants was assessed using biometric and biochemical parameters such as length, fresh weight, dry weight and electrolyte leakage. The high-resolution spectral data were obtained using a multichannel spectrometer in the visible and near infrared ranges of the electromagnetic spectrum in 128 channels at a spectral resolution (halfwidth) of 2.6 nm. Using the technique which employs discriminant analysis and other statistical methods we established the presence of statistically significant differences in the arising variations of the leaf spectral reflectance characteristics between control and treated plants in the green (520+580 nm), red and near infrared (690+800 nm) ranges of the spectrum.

Effects of Salinity on Leaf Spectral Reflectance and Biochemical Parameters of Nitrogen Fixing Soybean Plants (Glycine max L.)

Measurements of physiology and hyperspectral leaf reflectance were used to detect salinity stress in nitrogen fixing soybean plants. Seedlings were inoculated with suspension of Bradyrhizobium japonicum strain 273. Salinity was performed at the stage of 2nd–4th trifoliate expanded leaves by adding of NaCl in the nutrient solution of Helrigel in concentrations 40 mM and 80 mM. A comparative analysis was performed between the changes in the biochemical parameters ‐ stress markers (phenols, proline, malondialdehyde, thiol groups), chlorophyll a and b, hydrogen peroxide, and leaf spectral reflectance in the spectral range 450–850 nm. The spectral measurements were carried out by an USB2000 spectrometer. The reflectance data of the control and treated plants in the red, green, red‐edge and the near infrared ranges of the spectrum were subjected to statistical analysis. Statistically significant differences were found through the Student’s t‐criterion at the two NaCl concentrations in all of the ranges examined with the exception of the near infrared range at 40 mM NaCl concentration. Similar results were obtained through linear discriminant analysis. The tents of the phenols, malondialdehyde and chlorophyll a and b were found to decrease at both salinity treatments. In the spectral data this effect is manifested by decrease of the reflectance values in the green and red ranges. The contents of proline, hydrogen peroxide and thiol groups rose with the NaCl concentration increase. At 80 mM NaCl concentration the values of these markers showed a considerable increase giving evidence that the soybean plants were stressed in comparison with the control. This finding is in agreement with the results from the spectral reflectance analysis.Measurements of physiology and hyperspectral leaf reflectance were used to detect salinity stress in nitrogen fixing soybean plants. Seedlings were inoculated with suspension of Bradyrhizobium japonicum strain 273. Salinity was performed at the stage of 2nd–4th trifoliate expanded leaves by adding of NaCl in the nutrient solution of Helrigel in concentrations 40 mM and 80 mM. A comparative analysis was performed between the changes in the biochemical parameters ‐ stress markers (phenols, proline, malondialdehyde, thiol groups), chlorophyll a and b, hydrogen peroxide, and leaf spectral reflectance in the spectral range 450–850 nm. The spectral measurements were carried out by an USB2000 spectrometer. The reflectance data of the control and treated plants in the red, green, red‐edge and the near infrared ranges of the spectrum were subjected to statistical analysis. Statistically significant differences were found through the Student’s t‐criterion at the two NaCl concentrations in all of the ranges examined...

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 2nd to 4th 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 Students 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.

Hyperspectral remote sensing of the impact of environmental stresses on nitrogen fixing soybean plants (Glycine max L.)

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 days seedlings were inoculated with suspension of Bradyrhizobium japonicum strain 273. Salinity was performed at growth stage of 2nd– 4th 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 14th 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 Students 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.

Remote Sensing Study of the Influence of Herbicides Fluridone and Acifluorfen on the Spectral Reflectance of Pea Plant Leaves (Pisum sativum L.)

Results from a remote sensing study of the leave spectral reflectance of pea plants (Pisum sativum L. cultivar Scinado) treated by the photosynthetic herbicides fluridone and acifiuorfen are presented. According to the mode of action, fluridone belongs to Fl (photobleaching) group of herbicides, and acifiuorfen -to the group E as classified by the Herbicide Resistance Action Committee. The pea plants were grown hydroponically in a growth chamber in a nutritious medium to which the herbicides were added at two low concentrations (1 muM, 0.1 muM for fluridone, and 25 muM, 2.5 muM for acifiuorfen). The high-resolution spectral data were obtained in the visible and near infrared ranges of the spectrum (450/850 nm) using a USB2000 fiber optic spectrometer at a spectral resolution (halfwidth) of 1.5 nm. After data analysis, optimal spectral intervals for evaluation of the herbicide action were specified. The changes occurring in the spectral reflectance of the pea plants were assessed in four intervals: 520/580 nm (region of maximal reflectivity of green vegetation), 640/680 nm (region of maximal leave absorption), 690/720 nm (red edge region), and 720/770 nm (near infrared region) using the t-criterion of Student and linear discriminant analysis. Statistically significant differences were found between the spectral reflectance data of leaves of control and treated with herbicides plants at a significance level p<0.05 for the two fluridone concentrations and for 25 muM concentration of acifiuorfen. The applied approach provides fast and reliable remote sensing of plant response to the environment.

Effects of Salinity on Chlorophyll Fluorescence of Nitrogen Fixing Soybean Plants (Glycine max L.)

Leaf chlorophyll ffluorescence was measured in order to assess the effect of salinity on nitrogen fixing soybean plants. Three day’s seedlings were inoculated with suspension of Bradyrhizobium japonicum strain 273. The plants were grown at nutrient solution of Helrigel and salinyzed at stage of 2nd trifoliate expanded leaves by adding of NaCl at concentrations 40 mM and 80 mM. The chlorophyll fluorescence was registered by an USB2000 spectrometer in the spectral range 600–850 nm. As a source of actinic light a light emitting diode with the maximum of the light output at 470 nm was used. The course of the fluorescence spectra and the slow transient fluorescence kinetics were investigated. The Student’s t‐criterion and discriminant analysis were applied to estimate the changes between fluorescence spectra of control and treated soybean plants in five characteristic wavelengths in the spectral range 600–850 nm. Statistically significant differences were established by the t‐criterion at p<0.05 for data at th...

Response of chlorophyll fluorescence to salinity stress on the early growth stage of the soybean plants (Glycine max L.)

The chlorophyll fluorescence in response to salinity stress of soybean plants in spectral range 650–850 nm and slow transient fluorescence kinetics were investigated using remote sensing techniques. The soybean plants were grown under controlled conditions as water cultures on nutrient solution of Helrigel. Salinity was performed at the stage of 2nd to 4th trifoliate expanded leaves by adding of NaCl in the nutrient solution at concentrations 40 mM and 80 mM. The chlorophyll fluorescence was registered by a multichannel fiber optic spectrometer USB2000 working in time-acquisition mode. As a source of actinic light, a light emitting diode with the maximum of the light output at 470 nm was used. The fluorescence spectra were registered subsequently in time at every 2 second. At least 40 spectra from each soybean leaf were obtained; the leaves being taken from 20 control plants and 20 plants treated with two NaCl concentrations. Measurements were conducted on the 14th day after treatment. Several indices such as fluorescence spectra area, halfwidth of the fluorescence spectral curve, and wavelength of spectrum maximum were used to characterize the differences between the normalized fluorescence spectra of leaves of control and treated plants. The Student t-criterion, discriminant analysis and derivative analysis were applied to estimate the statistical significance of the differences between the average values of the indices. The results revealed that the low NaCl concentration led to salinity tolerance while the high NaCl concentration caused salinity stress in the soybean plants.

Investigation of the vertical profile of the aerosol scattering in the atmosphere by multichannel data from space station MIR

Abstract An approach is suggested and applied to determine the atmospheric optical depth parameters from spectral solar irradiance data provided by the multichannel trace spectrometric system “Spectrum 256”. The system “Spectrum 256” has been designed by scientists from the Solar-Terrestrial Influences Laboratory at the Bulgarian Academy of Sciences and has been operated onboard the MIR space station since 1988. By scanning the atmosphere with the spectrometer pointed directly at the Sun as the MIR station passed from the terminator zone to the sunset zone, the distribution of the atmospheric optical depth components in a vertical column of the Earths troposphere in the layer between 2 km and 14 km was determined. The molecular (Rayleigh) scattering was modeled and the aerosol scattering model parameters were evaluated. The selective absorption due to gaseous components and water vapor in the 475–810 nm spectral range was determined, taking into account the influence of the optical transmission characteristics of the hatches of the MIR station.

Chlorophyll fluorescence of nitrogen fixing soybean plants (Glycine max L.) under stress conditions

Chlorophyll fluorescence technique was applied on young nitrogen fixing soybean plants (Glycine max L.) for detecting and assessment of the effects of two environmental stress factors - salinity and enhanced UV-B radiation. Biological nitrogen fixation by legume - Rhizobium symbiosis is important to agricultural productivity and is therefore of great economic interest. Soybean and soy foods attract worldwide attention for their potential health benefits and uses in food manufacturing. Soybean plants were grown under controlled conditions as water cultures on Helrigel nutrient solution. Three days seedlings were inoculated with suspension of Bradyrhizobium japonicum strain 273. Salinity was performed at the stage of 2nd – 4th trifoliate expanded leaves by adding of NaCl in the nutrient solution in concentrations 40 mM and 80 mM. On the 14th day after the salinity treatment the half of the plants was treated with UV-B radiation at intensity of 64.4 µmol m−2 s−1 for four hours. Measurements were conducted on the same day. Hyperspectral fluorescence data were collected by a portable fiber-optic spectrometer in the visible and near infrared spectral ranges (600–900 nm). The spectral and statistical analysis was performed on fluorescence spectra normalized against the second maximum at five characteristic wavelengths. The statistical significance of the differences at p&#60;0.05 between data means of the control and treated plants were ascertained by the Students t-criterion. In the case of only salinity treatment the differences were statistically significant for both NaCl concentrations at all wavelengths with the exception of the rear slope. For the combined treatment (salinity + UV-B radiation) the differences in the spectra are non-significant at two of the wavelengths (in the middle of forefront and rear slope).

Use of a Remote Sensing Method to Estimate the Influence of Anthropogenic Factors on the Spectral Reflectance of Plant Species

Results from a remote sensing study of the influence of stress factors on the leaf spectral reflectance of wheat and tomato plants contaminated by viruses and pea plants treated with herbicides are presented and discussed. The changes arising in the spectral reflectance characteristics of control and treated plants are estimated through statistical methods as well as through derivative analysis to determine specific reflectance features in the red edge region.