反射率与叶绿素荧光遥感协同的冬小麦条锈病早期诊断研究

Solar-induced chlorophyll fluorescence (SIF) and xanthophyll cycle of plant are closely related to photosynthetic physiology. The two can be used as an early probe for plant physiological stress. Recent studies have shown that the SIF and lutein cycles at canopy level can be retrieved by hyperspectral remote sensing. Moreover, they have some advantages in the early detection of crop disease. However, their detection performance is restricted by canopy structure and environmental conditions and both theoretical and experimental studies are very weak. Firstly, the project is intended to obtain the fluorescence spectra, disease physiology and field meteorological data at different stages of winter wheat stripe rust disease, and explore the response characteristics of fluorescence spectrum, physiological and biochemical parameters under the stress of stripe rust. Secondly, spectral detection methods and models of biophysical, biochemical and physiological parameters, including SIF, lutein cycle, of winter wheat will be developed by means of the mechanism and model of spectral radiative transfer at canopy and leaf levels. Finally, we focus on exploring the coupling relationship between SIF and the photochemical reflectance index (PRI) at canopy level in the submersible stage of the stripe rust under different environmental conditions. Early diagnosis model of winter wheat stripe rust with fluorescence and reflectance remote sensing will be proposed by integrating fluorescence spectrum, physiological and biochemical spectral detection models for winter wheat stripe rust. It is expected that the research results are of great significance for predicting and mitigating crop diseases and accurate pesticide application.

植物日光诱导叶绿素荧光(SIF)和叶黄素循环与光合生理关系密切，二者可作为植物生理胁迫的早期“探针”。最近的研究表明冠层水平的SIF和叶黄素循环可以通过高光谱遥感反演，且在农作物病害早期探测中具有一定优势，但探测性能受冠层结构与环境条件影响和制约，理论和实验研究均十分薄弱。项目拟通过试验与模拟方法，获得冬小麦条锈病菌不同发展阶段的荧光光谱、病害生理及农田气象数据，探索条锈病胁迫下的荧光光谱特征和生理生化响应特征；然后，研究冠层和叶片的光谱辐射传输机理与模型，建立冬小麦生物物理、生化和生理参数(SIF、叶黄素循环)的光谱探测方法和模型；最后，重点探索不同环境条件下条锈病潜育期阶段的冠层SIF与光化学光谱指数PRI的耦合关系，集成冬小麦条锈病的荧光光谱特征、生理生化光谱探测模型等，建立荧光与反射率遥感协同的冬小麦条锈病的早期诊断模型。预期研究成果对预测和减缓作物病害与精准施药具有重要意义。

防治作物病害的关键在于治早。在病害早期阶段，植物更多的是通过生理机制的调整来快速适应环境胁迫。叶绿素荧光和热耗散都是植物光合作用与光保护机制的重要组成部分，是环境胁迫下植物受胁状态及植物生理、光合作用状况的直接“探针”。项目聚焦“冬小麦条锈病早期遥感诊断”这一重要科学问题，开展了野外田间试验与理论模拟研究。基于田间试验，观测了条锈病不同发展阶段下冬小麦冠层反射、日光诱导叶绿素荧光(Solar-Induced Chlorophyll Fluorescence, SIF)光谱，以及生化生物物理参数；采用SCOPE模型模拟了生理、生化、冠层结构及环境因素对冬小麦冠层SIF的贡献；探索基于单一反射信号或叶绿素荧光特征在诊断冬小麦条锈病的各自特点，并重点研究了反射光谱与SIF的耦合关系，最后协同反射率与冠层SIF构建冬小麦条锈病早期诊断模型。研究主要结果如下：（1）冬小麦从条锈病发病初期至末期，冠层持续失绿，随着发病阶段推进，LAI持续减小，叶绿素浓度快速下降，荧光动力学参数Fv/Fm和ΦPSII持续下降。（2）随着病害程度的加深，冠层红光附近的反射率呈现上升趋势，近红外波段则大幅降低；连续叶绿素荧光745nm和687nm附近“双峰”随着病情指数增加而降低，且745nm荧光峰出现“蓝移”现象。（3）基于理论模拟表明，叶绿素浓度及LAI对SIF的贡献排名前二，均超过40%。（4）PRI、NDVI和CI等反映植被生理、冠层结构、叶绿素含量都与条锈病病情指数呈极显著负相关水平；SIF无论是绝对强度还是相对强度，3FLD760.5以及比值3FLD760.5/686.8均与病病情指数达到了极显著负相关；绝对SIF导数光谱指数在诊断条锈病时不如相对SIF导数光谱指数；连续SIF光谱中包含着更丰富的信息，能够更敏感地反映植被受胁迫状态。（5）项目通过耦合反映生化、冠层结构等信息的CI、NDVI等反射光谱指数及对植物光合功能及受病害胁迫状况敏感的SIF及PRI，构建了冬小麦条锈病早期诊断的混合指数及模型（PRI/NDVI+SIF*CIred-edge/NDVI）。本项目研究成果对预测和减缓冬小麦条锈病的发生流行，降低防治成本和病害损失，减轻环境负荷等方面具有重要意义。