High-throughput Phenotyping Of Photosynthesis And Evaluation Of Yield-Quality In Oilseed Rape

As the most important physiological process affecting the growth and development of crops,photosynthesis is considered as the most direct expression of crop growth state,and its changes can not only directly and effectively reflect the growth and stress status of crops,but also affect the global balance of carbon,water and other materials.Therefore,rapid,non-destructive and accurate dynamic monitoring of photosynthesis is crucial for intelligent field management and crop yield and quality evaluation.Although the traditional gas exchange based method on the measurement of photosynthetic phenotypic parameters has been well established,which is inefficient and time-consuming and difficult to gain a more in-depth understanding of the inevitable link between changes in biochemical reactions and ambient environment on a spatial and temporal scale.With the rapid development of proximal optical property sensors,they are gradually regarded as an efficient plant phenotype sensing technology and have made certain achievements.However,the current plant photosynthetic phenotypic trait assessment based on near-ground reflectance mapping technology still suffers from poor resolvability,weak generalization ability and difficulty in leaf-to-canopy upscaling.In view of this,this paper takes oilseed rape as the research object and aims to obtain photosynthetic and yield quality phenotypic information in a comprehensive,efficient and accurate manner.We adopted the cross-scale research method of"organ-plant-canopy"to explore the vertical differences in photosynthetic physiological responses of leaves and siliques of oilseed rape during different growth stages.The method for yield and quality traits assessment of oilseed rape based on chlorophyll fluorescence technology was established.We have established an automated crop canopy fluorescence（Solar/Sun-induced chlorophyll fluorescence,SIF）monitoring system to expand the observation scale of crop photosynthetic phenotypic trait assessment.The diurnal and seasonal variations of canopy SIF and canopy reflectance spectral traits of oilseed rape were explored through field experiments,thus providing novel methodological ideas and technical support for accurate monitoring of crop phenotypic information,precise management of farmland and intelligent breeding..The main research contents and conclusions of this paper are summarized as follows:（1）In view of the lack of mechanical explanation in crop photosynthetic and yield and quality traits evaluation using reflectance mapping technology,the differences in vertical distribution of biochemical parameters,photosynthetic physiology,yield and quality parameters and nitrogen response of oilseed rape leaves and siliques were investigated.The results showed that the chlorophyll fluorescence parameters related to light energy capture and energy dissipation in the top layer had a high and positive correlation with leaf chlorophyll and carotenoid contents,and were positively affected by higher nitrogen treatment levels.In addition,the coefficient of determination（r²）and the relative root mean square error（r RMSE）of chlorophyll fluorescence technology were about 0.7 and 15%,respectively.In terms of quality traits evaluation,the results of oil and protein content assessment were also acceptable（r²=0.8,r RMSE=7.2%and r²=0.76,r RMSE=12%）.（2）Aiming at the problems of low measurement efficiency and labor-intensive in the evaluation of photosynthetic traits using gas exchange based technology,an automatic and high-throughput observation system for crop canopy sun-induced chlorophyll fluorescence measurement in the field was developed.The results showed that the system could accurately and efficiently capture the photosynthetic physiological dynamics of crops in different growth stages.It proved that the crop canopy SIF was more sensitive to diurnal and seasonal changes than normalized difference vegetation index（NDVI）.Especially for the seasonal dynamics,the variation trend of canopy SIF was consistent with that of leaf photosynthetic fluorescence parameters.In addition,by discussing the current development status of crop phenotypic traits monitoring system,and summarizing the problems and difficulties existing in different phenotypic traits monitoring platforms,the idea of building and upgrading the automatic observation system of canopy SIF was also proposed,and the process of instrument design,installation,wavelength and absolute radiation calibration of the system was introduced in detail.It provides a basis for the system to migrate to other farmland ecosystems,and also provides an efficient,integrated and large-scale solution for crop canopy photosynthetic phenotype assessment.（3）Due to the difficulty of automatic monitoring and analysis during the entire growth stages of crops in the field environment,automatic monitoring of canopy reflectance spectra and fluorescence properties during the whole growth stages was carried out,and the correlation among the canopy SIF,VIs and NPP was analyzed.The results showed that the linear relationship between SIF-NPP（r²=0.75,RMSE=0.11）was always better than that between NDVI-NPP（r²=0.08,RMSE=0.21）during the whole growth period,which proved the advantage of canopy SIF in crop net primary productivity assessment.In addition,the correlation between canopy SIF-NPP was higher in the early growth stages（seedling and bolting stage）than in other growth stages.However,the correlation between canopy SIF-NPP was reduced in the flowering stage and late silique stage due to great changes in canopy color and structure.Moreover,different temporal resolutions also showed significant impacts on the correlation between canopy SIF-NPP.In general,higher correlation between canopy SIF-NPP could be obtained with per hour sampling resolution.The results provide a reference for crop canopy reflectance spectrum and fluorescence traits monitoring based on UAV and other platforms.（4）Aiming at the difficulty of crop leaf to canopy scale conversion,the up-scale study of leaf and silique photosynthesis and yield and quality phenotype in oilseed rape was carried out to analyze the potential relationship between leaf and silique photosynthetic physiology and canopy phenotype.The results showed that crop canopy structure factors could significantly affect the correlation between leaf photosynthetic parameters and canopy fluorescence.Compared with original canopy SIF,both canopy SIF/LAI and SIF/LAP could improve the evaluation of leaf and yield traits to canopy photosynthetic phenotypes.A linear model between canopy fluorescence and leaf photosynthetic and yield traits was constructed.In addition,the evaluation ability of leaf photosynthetic pigment content on leaf photosynthetic parameters in different growth stages was also analyzed,and the influence of leaf pigment content in different growth stages on the photosynthetic process was also analyzed.The coefficients of determination between the absorbed photosynthetically active radiation（APAR）and V_cmax and J_max were higher than that of photosynthetically active radiation（PAR）respectively,indicating that APAR affected the photosynthetic process more deeply.The results are helpful to improve the evaluation strategies for photosynthesis processes at different scales,and can provide reference for crop photosynthetic phenotypes monitoring and new breeding methods developing based on SIF technology.