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 2(nd) 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 the first three wavelengths (at the middle of the leading edge, first maximum and at the middle of the first and second maximum) for both NaCl concentrations The discriminant analysis confirmed these findings A comparative analysis was performed with leaf spectral reflectance of the same plants collected in the spectral range 450-850 nm by the same spectrometer All measurements were performed on the 14(th) day after the salinity treatment The results from the implementation of the two remote sensing techniques (chlorophyll fluorescence and spectral reflectance) revealed that both NaCl concentrations brought to salinity stress in the nitrogen fixing soybean plants.