Research On Physiological Status Monitoring System Of Tea Seedling Based On Fluorescence Image

The addition of emerging technologies such as remote sensing and image processing has made modern agriculture more informative and intelligent.Rapid and accurate access to crop growth information is an important prerequisite for the development of modern agriculture,and targeted guidance of cultivation based on the information will be the future development trend of agriculture.Chlorophyll fluorescence,as a non-destructive detection probe for plants,is widely used in plant physiological state monitoring,stress and disease detection,etc.In this paper,starting from the mechanism of chlorophyll fluorescence generation,we designed a high uniformity excitation array and built a fluorescence acquisition system to analyze the correlation between fluorescence parameters,relative chlorophyll content and image parameters of tea seedlings under drought stress,as follows.（1）The mechanism of chlorophyll fluorescence generation and absorption emission spectra were studied,and the method of using fluorescence kinetic curves to obtain fluorescence parameters to assess plant growth status was discussed.The fluorescence emission system and acquisition system were selected and built.The fluorescence images under time series were acquired,and the chlorophyll fluorescence-induced kinetic curves were obtained by grayscale extraction of the fluorescence images.（2）The ratio of the minimum irradiance to the average irradiance in the sample area is proposed as the irradiance uniformity index,and the irradiance simulation analysis and experimental validation are carried out for the basic LED arrays with different array parameters based on the same observation plane.The results show that the spatial irradiance uniformity of LEDs is positively correlated with the array spacing and height.The optimal LED array parameters were selected by combining the empirical equation of the LED central irradiance uniformity with the experimental conditions,and the excitation light source of the chlorophyll fluorescence imaging system was built.（3）Tea tree seedlings from southern Shaanxi Province were selected as experimental samples and the correlation between fluorescence parameters and drought stress was analyzed.The experiments showed that the fluorescence decay ratio(R_fd)of isolated tea seedlings was highly correlated with the time of drought stress,and the adjusted coefficient of determination was 0.98.The regular changes of each parameter in living seedlings during 7 days of drought stress were investigated and the corresponding models were established to evaluate the correlations,in which the time of fluorescence sub-peak appearance（TF_m’）and dynamic fluorescence index（DFI）were better fitted,and the adjusted coefficients were 0.84 and 0.82,respectively.The adjusted coefficients of determination were 0.84 and 0.82,respectively.（4）SPAD values of tea tree seedlings under different components were measured by SPAD meter and found to be positively correlated with drought stress time by Pearson correlation analysis and linear fitting.The color components in different color spaces were investigated,and it was found that four parameters R,G,B and I were highly significantly correlated with fluorescence intensity,and parameters H,R/B,G/B and I/（H+I）were strongly correlated with fluorescence intensity at the 0.01 level,with Pearson coefficients greater than0.90.Tea seedlings with different components and different days of stress were pseudo-colored to show the changes of fluorescence characteristics and plant physiological status under drought stress in two-dimensional scale direction.The use of fluorescence images to monitor the physiological state of plants provides a new idea of auxiliary detection for the development of precision agriculture.