Analysis on drought stress of Longjing tea seedlings based on slope fluorescence index

Drought stress is the main factor affecting plant grown and development. Chlorophyll fluorescence was chosen as research object to study the effects of drought stress on the growth of Longjing tea seedlings crops. A chlorophyll fluorescence collection system was designed with LED, CCD and filter. Longjing tea seedling with good growth were selected for drought treatment. The tea seedlings should be dark treatment before each experiment. Using LED lamps actively induced the emission fluorescence of tea seedlings, and the images were collected in the same time period for 8 consecutive days. The chlorophyll fluorescence quenching curve was drawn through the mean gray value of the images after preprocessing with median filter. We proposed a new method for evaluating fluorescence quenching curves using slope index, named the slope fluorescence index (SFI). The range of the gray scale mean at the same time in 1-8 days is calculated, the relative errors of range were calculated over the selected time range and determining the time range of range stability. Within the time range, correlation model between each point on the curves and the stress days was established to find a point with the largest correlation coefficient R 2 . The results showed that there was the highest correlation between the SFI of fluorescence quenching curve at 327s and the days of drought stress (determinant coefficient R 2=0.94021). Slope fluorescence index (SFI) is used to evaluate chlorophyll fluorescence quenching curve, which will provide a new idea for monitoring plant growth under stress.