Characterization Of Chlorophyll Fluorescence-reflectance And Spatiotemporal Heterogeneity In Crop Physiological/Biochemical Phenotypes

The rapid acquisition of crop physiological and biochemical phenotypic information（such as pigment content,dry matter content,water content,photosynthetic rate,etc.）is of great significance to corp breeding,field management,and ultimately to achieve high-quality and high-yield.At present,many phenotypic methods have been developed for crop physiological and biochemical information monitoring,however,the current acquisition of phenotypic information mainly focused on the collection and analysis of single-level information such as crop canopy or leaves,and there are still limitations in the acquisition and integration of multi-dimensional information such as crops at different levels of leaves and different growth periods.Therefore,quantitative research and analysis of the vertical heterogeneity of physiological and biochemical information in the crop canopy are carried out to explore the nutrient transfer and distribution and spectral response of crop leaves in different growth stages and leaf layers,and to reveal the monitoring mechanism of the spatiotemporal heterogeneity of crop growth information.It is of great significance for the future use of phenotypic technology to estimate crop growth information,and provides effective theoretical methods and technical support for the implementation of dynamic monitoring of crop growth information and precise scientific fertilization.In this study,we mainly focused on typical monocot crops of rice and dicot crops of rape,measured biochemical parameters such as chlorophyll content,carotenoid content,dry matter content and moisture content during the whole growth period of the crop under different nitrogen treatments,explored the photosynthetic physiological response of crops using rapid chlorophyll fluorescence technology,combined crop biochemical parameters and photosynthetic physiological with hyperspectral technology,analyzed the biochemical parameters,fluorescence response,and the inner link between them,and investigated the use of crop canopy spectra in different leaf layers of physiological and biochemical information for regression analysis.The main research contents and results are as follows:（1）The spatiotemporal heterogeneity of crop biochemical parameters was analyzed,and the regulation of source-sink relationship and nitrogen response during vegetative and reproductive growth stages were clarified.Rice had a specific vertical distribution pattern of chlorophyll and carotenoid content during a specific growth period.During the vegetative phase,it showd a vertical gradient that gradually decreased from the lower layer to the upper layer,and changed to a gradually increasing vertical distribution after entering the reproductive growth period.Nitrogen application rate would affect the time point of the transformation of this vertical distribution pattern,that is,nitrogen deficiency and excessive nitrogen shorten and prolonged the duration of the vegetative phase,respectively.Rice leaf chlorophyll/carotenoid did not have significant vertical heterogeneity among different leaf positions,while the leaf chlorophyll a/b value showed a vertical heterogeneity that gradually increased from the lower layer to the upper layer,which also reflected the fact that the lower layer leaves required a larger antenna size due to receiving less light.In addition,the chlorophyll/carotenoid and chlorophyll a/b values were hardly affected by the level of nitrogen application.The contents of chlorophyll,carotenoid,dry matter and water in the canopy of rapeseed at seedling stage showed a parabolic vertical distribution,and the contents of chlorophyll and carotenoid in the middle stage were the highest,while the contents of dry matter and water were the lowest.However,the ratio of chlorophyll to carotenoid decreased with the increase of leaf position and nitrogen application rate,and the antenna size of basal leaves was significantly larger than that of middle and parietal leaves.The vertical distribution patterns of biochemical parameters of rice and rapeseed were different,and there were different response mechanisms in the utilization of light energy.（2）The spatiotemporal heterogeneity of chlorophyll fluorescence response in crops was explored,and the relationship between different biochemical characteristics and photosynthetic functions of crops was compared.Under different nitrogen treatments,the photosynthetic characteristics of rice canopy had a specific vertical distribution pattern at certain key growth stages（tillering,jointing,initial heading,and late filling stage）,and the specific vertical distribution pattern could be used to detect the nitrogen stress effectively.The photosynthetic vertical distribution pattern at the seedling stage of rape was close to that at the later stage of rice grain-filling,which reflected the similar canopy light distribution and vertical distribution of biochemical components in the two stages.The JI phase in the OJIP transient curve of rice leaves showed an unusual decline during the vegetative phsae,but a normal rise during the reproductive phase,which may be an indicator to distinguish the functions of leaves as‘sink’or‘source’.The change of OJIP curve was two stages earlier than that of chlorophyll content.The active PSII reaction center（RC/CS）and photosynthetic performance(PI_ABS)of JIP-test parameters can indicate the leaf age of rice,while the energy absorbed（ABS/RC）and dissipated（DI₀/RC）per active reaction center can describe the vertical light distribution in the canopy.The JIP-test parameters related to PSI electron transport efficiency,RE₀/CS and DF_Total,were the most relevant photosynthetic parameters for each biochemical component of rice and oilseed rape,respectively,and could be used as potential sensitive indexes to characterize physiological and biochemical vertical heterogeneity in canopy.Crops under different nitrogen treatments have significant temporal and spatial heterogeneity of photosynthetic physiology and distinct characteristics of growth period,and the fluorescence response can also effectively characterize the temporal and spatial heterogeneity of crop biochemical parameters.（3）The spatiotemporal heterogeneity of crop reflectance spectra was studied,and the relationship between leaf/canopy spectra and different biochemical parameters and JIP-test parameters was established.Rice reflectance spectra had significant heterogeneity of space and time,as in the vegetative phase（initial tillering to jointing stage）,rice leaf reflectance spectra under three nitrogen treatments were increased with the increase of leaf position its reflectance,and reproductive growth stage of early earing,its reflectance began to decrease with the increase of leaf position.There were significant differences in leaf reflectance spectra at 1450 nm between rice and oilseed rape due to different leaf structures.However,the vertical distribution pattern of mean reflectance spectra at each leaf position in rape seedling stage was the same as that in rice,and the lower leaves of rape contributed more to canopy spectra.ABS/RC and TR₀/RC have a higher positive correlation with the region of 1350-1900 nm and 1980-2400 nm,whileγ_RC has a higher negative correlation with the region of 500-700 nm,1400-1900 nm and 1980-2400 nm.Canopy reflectance was also highly correlated with biochemical parameters and photosynthetic physiology of different leaf positions of oilseed rape,reaching 0.8 and 0.6,respectively.Therefore,the physiological and biochemical information of different leaf layers of rape could be effectively estimated by canopy spectrum.