Study On The Spectral Characteristics Of Winter Wheat Under Low Temperature Stress

In this study,the physiological and biochemical indexes of leaves and the original spectral characteristics of winter wheat were analyzed by artificial simulated low temperature stress test on winter wheat in the regreening stage and jointing stage.The physicochemical parameters of the significant test were used to establish the correlation between the physical and chemical parameters of the leaves and the original spectral reflectance of the leaves,the first-order differential values of the spectral reflectance of the leaves and the vegetation index.The feature parameters with the largest coefficient of determination are selected to construct an estimation model based on the physical and chemical parameters of hyperspectral,and the model is verified by the measured data.The results of this study provide basic data support for the use of high-spectrum and convenient monitoring of winter wheat frost damage.The conclusions are as follows:(1)After low temperature stress,the chlorophyll a,chlorophyll b,total chlorophyll content,SPAD value and photosynthetic rate of winter wheat in jointing stage were tested by significant difference.Therefore,the above indicators were selected as the physical and chemical parameters for studying low temperature stress of winter wheat.After the same degree of low temperature stress in winter wheat under different fertility and density conditions,the total chlorophyll content of winter wheat leaves decreased under low fertilizer conditions.Under the condition of medium fertilizer,the total chlorophyll content of winter wheat leaves increased and decreased,and the total chlorophyll content of winter wheat leaves increased under high fertilizer conditions.Compared with the control group,the total chlorophyll content of winter wheat decreased by 10%after 2h of low temperature stress,and the total chlorophyll content decreased by 26.2%after 4h of low temperature stress.The total chlorophyll content of leaves decreased by 14.0%after 6h of low temperature stress and the total chlorophyll content decreased by 5.6%after 8h of low temperature stress.The SPAD value of winter wheat in the regreening stage increased by 16.4%at Oh after 8h of low temperature stress.The SPAD value of winter wheat at jointing stage increased by 7.2%at Oh after 6h low temperature stress,and the SPAD value decreased by 29.2%after Oh at 8h.The MDA content of winter wheat under different fertility and density conditions decreased and increased after the same low temperature stress.The MDA content of winter wheat under normal planting conditions showed a downward trend after low temperature stress.The decrease of photosynthetic rate of winter wheat leaves after chilling stress at 8h after regreening and jointing was caused by stomatal limitation.The photosynthetic rate of winter wheat in jointing stage after 6h low temperature stress was caused by non-stomatal limiting factors.(2)The analysis of the original spectral reflectance of winter wheat leaves under low temperature stress can be found that the winter wheat in the regreening period can be effectively distinguished from low temperature stress,and the different recovery time of winter wheat after cold stress can be distinguished.In the regreening period,the amplitude and area difference of the blue edge are 0.0009 and 0.0199,respectively.In the jointing stage,the amplitude and area difference of the blue edge are 0.002 and 0.0377,respectively.In the "three-sided" parameters,the amplitude and area of the blue and yellow sides are sensitive to different degrees of low temperature stress,and the blue edge parameter is the most sensitive parameter to low temperature stress.(3)Correlate the physical and chemical parameters of the significance test with the original spectral reflectance of the blade,the first-order differential value of the spectral reflectance,the constructed ratio vegetation index and the difference vegetation index,and select the largest decision coefficient and pass the significance test.The parameter construction is based on a hyperspectral physicochemical parameter content estimation model.The estimated model was randomly selected to verify the estimation model.The estimation model with the root mean square error and the smallest relative error was selected as the optimal estimation model.The final estimation model of SPAD content based on hyperspectral winter wheat leaves was CSPAD=273.9XRVI[735,803]-257.47?In this study,the physicochemical parameters and hyperspectral parameters of winter wheat leaves after low temperature stress were selected to establish the estimation model of the physical and chemical parameters.Through the establishment of the estimation model,more abundant experimental data were provided for hyperspectral monitoring of freezing damage.