Hyperspectral Response Mechanism And Monitor On Physiological Parameters Of Winter Wheat Under Low Temperature Stress

The variety of "Linmai 7006" was selected as the research object,and was conducted with the field plot test.In study,the winter wheat was treated under low temperature stress at jointing stage,and the main physiological parameters and canopy spectral reflectance of winter wheat were measured at certain days after the jointing stage.The change law for the physiological parameters and the spectral reflectance were analyzed,the spectrum was transformed with respect to 15 transformation methods,and the winter wheat physiological parameter monitoring model was finally constructed with partial least squares method to determine the optimal spectral transformation method which can accurately and quickly invert the winter wheat physiological parameters.Moreover,the microstructure of winter wheat leaves under low temperature stress was observed to explore the hyperspectral response mechanishm on the winter wheat under low temperature stress.The results showed that:1.The physiological parameters of winter wheat(chlorophyll content,aboveground dry biomass,leaf photosynthetic rate,leaf stomatal conductance)under the same low temperature stress showed the same pattern of variation.With the increased of the level of low temperature stress,the physiological parameters(chlorophyll content,aboveground dry biomass,leaf photosynthetic rate,leaf stomatal conductance)of all treatments were lower than the controls,and were more obvious in the short term,and the leaves intercellular CO2 concentration was higher than the controls after the 5 days later.After stress 10 d,20 d,and 35 d,the differences between the physiological parameters and the controls were gradually reduced.2.The changes of the raw spectral reflectance of winter wheat under different low temperature stresses were basically same.After stress 5 days,the spectral reflectance both increased in the visible wavelength region and in the near infrared region.Compared with the control group,the spectral reflectance significantly increased after the low temperature stress.After stress 10 days and 20 days,the spectra changes were almost the same.After stress 35 days,the visible region tends to be flat and the red valley arisesd.The spectral reflectance in the near infrared region gradually decreases among all treatments.3.After the 5 days of low temperature stress,the leaf mesophyll cells of winter wheat shrank and cell gaps extended.After a number of days of low temperature stress,the cell shrinkage became smaller and the cell gap also followed.4.Compared with the original spectra(To),the spectral features was not obvious for the transformed spectra without differential processing(such as reciprocal,logarithm,power,square root,etc.),while for these transformed spectra related to differential processing were significant.Compared with the original spectrum,the correlation coefficient between the winter wheat physiological parameters and the transformed spectrum was significantly improved,especially for the correlation between the above-ground dry biomass and the transformed spectrum,which could reach to 0.9.5.Compared with the raw spectrum,the spectral transformation without differential processing(such as reciprocal,logarithm,power,square root,etc.)is difficult to improve the correlation with winter wheat physiological parameters,and their models were also poor.The model based on the second-order differential transformation(T15)performed best with R2=0.990,RMSE=379.184,RPD=10.068 for the aboveground dry biomass monitoring model;R2=0.932,RMSE=0.205,RPD=3.898 for chlorophyll content;leaf photosynthesis rate is R2=0.907,RMSE=0.664,RPD=3.339,and small of the number of factor variables were introduced into the monitor model with Fn=3.It showed that the transformed spectral based on the method of T15 could achieve good spectral estimation on physiological parameters of winter wheat(chlorophyll content,aboveground dry biomass,leaf photosynthetic rate).Moreover,the second-order differential of the inverse of the logarithm of the original spectrum(T10)and the second-order differential after the square of the original spectrum(T11)could also be considered for the spectral monitor on the winter wheat after the low temperature stress.However,The fifteen spectral transformation methods were not always suitable for estimating the stomatal conductance and intercellular CO2 concentration of winter wheat leaves under low temperature stress.