Monitoring Chlorophyll Content And Drought Stress In Rice Using Sun-induced Chlorophyll Fluorescence

Chlorophyll fluorescence is closely related to vegetation photosynthesis,which can accurately reflect the chlorophyll status of plants and early monitoring of plant environmental stress.This study was based on field trials of different growth stages,densities,and nitrogen levels in the whole growth period to obtain biological indicators,reflectance spectra,and suninduced chlorophyll fluorescence(SIF)in canopy and single leaf levels.SIF spectra and yield indices were extracted,and the best SIF index for monitoring canopy and single leaf chlorophyll content was screened to construct a rice chlorophyll content monitoring model,which further analyzed the SCOPE model and the Fluspect-B model in canopy and single leaf.Retrieving the performance of chlorophyll content on a scale.At the same time,based on the barreling experiment of drought stress treatment in rice tillering stage,the response of biological indicators,reflectance vegetation index and SIF index to rice drought stress was clarified,and then the most sensitive to drought stress in rice leaves was selected.Indicators and early identification of drought stress.The expected results can provide a theoretical basis for fertilization and irrigation in the precise management of rice.First,at the canopy and single leaf levels,the chlorophyll content was obtained using Dualex,and the SIF index of the canopy and single leaf levels was obtained using two hyperspectral instruments,ASD and QE Pro[the canopy was SIF intensity(F761,F687)and The single leaf is the SIF index(↑FY687,↑FY741,↓FY687,↓FY741)],the best SIF index is screened,and the chlorophyll content model of canopy and single leaf based on SIF index is constructed(F761 and NDFI,respectively);And compared with the prediction of chlorophyll content model by reflectivity vegetation index[NDRE,CI red edge,MTCI,LCI,mND705].A look-up table was constructed to invert the canopy and leaf chlorophyll content of the rice using the SCOPE and Fluspect-B radiation transmission models,and compared with the results of the two models using PROSAIL and PROCWT based on the hyperspectral reflectance.The results showed that the canopy SIF intensity F761 had the highest correlation with canopy chlorophyll content,the determination coefficient(R2)was 0.72,the fluorescence monitoring performance was slightly higher than the vegetation index,and the single leaf down SIF index ↓FY NDFI((↓FY741)-↓FY687)/(↓FY741+↓FY687))can be used for better monitoring of chlorophyll content(R2 is 0.77),the down-regulation fluorescence index is better than the up-fluorescence index,and the fluorescence monitoring performance is slightly higher than the vegetation index.Canopy PROSAIL(R2 was 0.91,Root mean squared error,RMSE was 22.59 μg/cm2),and the performance of rice canopy chlorophyll content was better than SCOPE(R2 is 0.57,RMSE is 56.54μg/cm2);single leaf PROCWT(R2 was 0.72,RMSE was 6.42μg/cm2),and the performance of rice leaf chlorophyll content was better than Fluspect-B(R2 is 0.55,RMSE is 19.45 μg/cm2).Further,the Li-6800 photosynthetic apparatus,Dualex,PAM2500 fluorometer and ASD hyperspectral ground reflectometer were used to obtain the biological index of leaf top leaf in the tillering stage[leaf water content(LWC),net photosynthetic rate(Photo),stomatal conductance(Cond),intercellular CO2 concentration(Ci),transpiration rate(Trmmol),chlorophyll index(Chl),anthocyanin index(Anth),photosystem II maximum photon yield(Fv/Fm)Reflectivity Vegetation Index[Normalized Vegetation Index(NDVI),Photochemical Vegetation Index(PRI),Red Edge Chlorophyll Index(CIred edge),Normalized Water Index(NDWI),Simple Ratio Water Index(SRWI),Water Index(WI)and SIF index[total fluorescence yield(FYtot),downward fluorescence yield(↓FY),downward yield at 687 nm(↓FY687),the ratio of downward SIF emission peaks(↓FY687/↓FY741)],to clarify the dynamics of the above indicators with the number of days of drought stress,and further use the analysis of variance,two classification and correlation analysis to screen out the most sensitive finger to drought stress in rice leaves.Early recognition and the ability to stress.The results showed that stomatal conductance and transpiration rate were the most sensitive to drought stress,and the earliest can identify the stress on the 4th day after the start of drought.PRI is the most sensitive to drought stress in the vegetation index,and can identify the stress on the 4th day after the start of drought;↓FY in the fluorescent SIF index was the earliest to identify drought stress on the third day after the start of drought stress.Based on the monitoring of chlorophyll content in rice and early monitoring of rice drought stress,SIF was found to have a good effect.In the monitoring of rice canopy and single leaf chlorophyll content,the SIF index showed slightly higher or equivalent to the traditional chlorophyll vegetation index.In the early monitoring of rice drought stress,the SIF index was able to identify the occurrence of drought stress.Therefore,sun-induced chlorophyll fluorescence can be used as a novel crop growth monitoring method for crop component content monitoring and early identification of stress states.