Remote Sensing Monitoring Mechanism Of Copper Stress In Rice Based On Solar Induced Fluorescence

One sixth of cultivated land in China has been polluted by heavy metals,and more than 12 million tons of food are polluted by heavy metal pollution every year,resulting in a loss of 20 billion yuan.It is of great significance for food security to carry out remote sensing monitoring of heavy metals in large areas of rice.Copper stress is different from other stresses.Under certain conditions,the pigments will not be destroyed,that is,the photosynthetic function of plants has been damaged,but the content of pigments has not decreased,so remote sensing inversion based on pigments may in errors.Chlorophyll fluorescence can detect changes sensitively in photosynthetic function which caused by stress,much earlier than changes in pigment content.The traditional laser-induced fluorescence monitoring of chlorophyll mainly focuses on the laboratory level.In this study,we combine plant physiology,hyperspectral remote sensing and solar induced fluorescence under rice stress.By observing the apparent reflectance and fluorescence characteristics of rice leaves,canopy and satellite layers,the extraction method of solar induced fluorescence was proposed,and the remote sensing inversion model of copper stress was established,and the accuracy of the model was verified.The purpose of this study was to improve the inversion accuracy of copper stress in rice and provide scientific basis of rice ecological environment for change monitoring.The main conclusions of this study are as follows:(1)The physiological and biochemical parameters of rice leaves changed with the concentration and stress time.The chlorophyll content of rice in the control and treated groups increased first and then decreased.On the one hand,copper ions promoted the chlorophyll content of vegetation,but with the stress time increases,the heavy metals inhibited the synthesis of chlorophyll,which led to the decrease of chlorophyll content.At the same time,water content also changes,heavy metal stress could cause the imbalance of water metabolism in plants,and water loss after stress.It is a manifestation of water metabolic disorder,and generally presents a normal distribution.(2)Different algorithms are used to extract chlorophyll fluorescence spectrum from reflectance spectrum.In the single leaf level,the apparent reflectance of leaves is subtracted from PROSPECT model by selecting the range of 580-650 nm where the fluorescence radiation of leaves is weak,and the reflectance spectra of leaves without fluorescence radiation are separated.In the canopy level,the Fraunhofer dark line with weak radiation is selected to calculate the fluorescence intensity by using FLD series algorithm.(3)It was found that the fluorescence spectra of rice leaves varied with copper concentration and stress time.The red fluorescence peak 686 nm of rice under copper stress was positively correlated with different copper concentration gradients(r=-0.876),while the far red fluorescence peak 760 nm was negatively correlated with copper stress intensity(r=-0.985),and the fluorescence ratio 686/760 nm was positively correlated with copper stress(r=0.903),that is,the fluorescence difference was more obvious than the apparent reflectance.(4)A copper stress inversion model was proposed.By analyzing the fluorescence spectrum curve induced by sunlight,it was found that the fluorescence index at 760 nm had a good correlation with copper stress.The best model is the one-dimensional quadratic polynomial model,which is applied to the image data to verify and analyze.The copper concentration intensity distribution near Dexing Copper Mine in Jiangxi Province is preliminarily obtained.