【作者】 张永江；

【导师】 王人潮； 赵春江；

【作者基本信息】 浙江大学 ， 农业遥感与信息技术， 2006， 博士

【摘要】 叶绿素荧光包含了丰富的光合信息,一直是光合生理研究的热点课题,被称为研究植物光合功能快速、无损伤的敏感探针。遥感作为大面积、快速获取目标性质的手段,近年来得到了突飞猛进的发展,在农业诸多领域都得到了广泛的应用。两者结合可以发挥各自优势。本研究以冬小麦为主要研究对象,分别在单叶和冠层不同尺度上,采用不同的算法提取表观反射信号中的荧光信息。结合荧光参数、叶绿素等生理生化参数测定,探讨不同水、肥、病胁迫下叶绿素荧光光谱特征特性,以及荧光指标与其他参数间的关系,分析荧光被动遥感应用于作物胁迫诊断的可行性。研究取得如下结果: 1.采用不同算法成功地从单叶表观反射光谱中提取到叶绿素荧光光谱。采用ASD光谱仪和LI-COR 1800-12S积分球耦合,光源模拟日光辐射,通过对积分球光源加与不加不同种类(长波通、短波通)截止滤光片的办法,获得不同光照条件下的叶片反射光谱,按照不同算法提取叶绿素荧光信息。结果表明利用长波通滤光片测得的表观反射率差值光谱可以代表荧光光谱,在红光区和远红光区表现为明显的双峰特征。采用短波通滤光片可直接获得荧光光谱,不同植物种类荧光光谱差异明显。透射光中也包含叶绿素荧光,检测剑的荧光相对比例大致与反射光荧光相近。结果验证了荧光对表观反射率光谱也有一定贡献的结论,并可以定量提取。 2.初步明确了冠层反射光谱中能够敏感反映叶绿素荧光的指标。日光诱导的叶绿素荧光,更真实地反映植物的生理状态。通过日变化试验,定点观测不同植物(小麦、地锦)的冠层光谱,并同步进行了叶绿素荧光参数测定。结果表明,表观反射率计算的曲率指数CUR、一阶导数光谱比值Dmax/D702以及生理反射指数PRI与荧光参数Fv/Fm变化趋势一致,一天中均呈现高—低—高的“V”字型变化;利用冠层辐照度光谱中688nm和760nm两个氧气吸收形成的夫琅和费暗线特征,可以计算太阳光诱导的光合作用荧光;荧光对PAR十分敏感,与荧光动力学参数FvPFm存在极显著的负相关关系,复相关系数达到了0.9以上。论文提出的利用野外地物光谱仪的辐照度模式观测的数据探测植被荧光,拓展了野外地物光谱仪的使用功能。 3.不同肥水条件下单叶、冠层荧光光谱特性存在差异。单叶水平表观反射率光谱中提取的荧光双峰比值Dif685/Dif740与荧光参数Fv/Fm关系密切,可以用来反映叶片含水量状况和叶片全氮含量。冠层水平表观反射率光谱中提取的PRI、红边区一阶导数比值、夫更多还原

【Abstract】 The chlorophyll fluorescence (CF) signature emitted from vegetation provides abundance of information of photosynthesis activity, and has been used as a powerful tool to obtain physiological information of plant leaves in a non-invasive way. Remote sensing (RS) can provide Earth’s surface information in large area and temporal period with different scales. So far RS has been widely applied in many fields in agriculture. The combination of CF and RS may take respective advantages. In this study, wheat (Triticum aestivum L.) was selected as the main material. First, the methods and algorithms were studied to separate CF from apparent reflectance spectra at leaf and canopy levels respectively. Then, CF from apparent reflectance spectra was analyzed with physiological and biochemical parameters such as CF parameters measured by modulated chlorophyll fluorometer, chlorophyll, etc. The main purpose was to study the chacteristics in fluorescence spectra at stress conditions (such as water and nitrogen deficiency, rust infected), as well as the influences on CF and other physiological and biochemical parameters made by stress factors. Finally, the potential of passive sensing of CF applied in crop stress detection was discussed. The results were summarized as below.1. Chlorophyll fluorescence spectra were successfully obtained from apparent reflectance spectra by special methods and algorithms. The leaves apparent spectra were measured under illuminations with and without specially designed filters, using a LI-COR 1800 integrating sphere coupled with an ASD spectrometer. Two kinds of filters (3 for long wave pass edge and 2 for short wave pass edge) were tested respectively. The results showed that fluorescence spectra could be derived from reflectance difference spectra under illuminations with and without long pass filter. Similarly, fluorescence spectra were derived from reflectance under illumination with short pass filters directly. Obvious differences in fluorescence spectra were founded in different kinds of plant. Additionally, CF was also detected from the transmittance spectrum and the relative scale was approximately close with that of the reflectance. The results confirmed the conclusion that CF was contributed to apparent reflectance to some extent and it could be separated quantificationally.2. The CF indices that closely related to apparent reflectance spectra at canopy scale were preliminary illustrated. The solar-induced CF can reflect real plant physiological status. Diurnal change experiments were conducted to measure canopy reflectance in wheat and Parthenocissus tricuspidata respectively, at the same time CF parameters were measured. The results indicated that CUR (curvature index), Dmax/D702 (the ratio of the first derivative at two bands) and PRI (physiological reflectance index) had the same tendency with Fv/Fm, which showed a characteristic of ’V type. Then, a method based on FLD (Fraunhofer line discriminator) was introduced to calculate solar induced fluorescence according to the molecular oxygen absorption by the terrestrial atmosphere at 688 and 760 nm. CF derived from FLD was sensitive to PAR, and had a notably negative relation with fluorescence kinetic parameter Fv/Fm (R~2>0.9). The paper provide a new method to detect vegetation fluorescence signals by radiance mode using field spectrometer, which extend the application scales of the instruments.3. The characteristics of fluorescence spectra at leaf or canopy levels exhibited differencesunder different N or water treatments. The ratio of the reflectance difference at 685nm and 740nm Dif685/Dif740 at leaf level was linear correlated with Fv/Fm and it could be an indicator to reflect leaf water or nitrogen content. At the canopy level PRI, Dmax/D702, FLD fluorescence present high correlationships with plant water content or canopy nitrogen density (CND). These indices have the potential to diagnose the water or nitrogen status in the fields, but the influence factors especially canopy structure should not be neglected.4. A preliminary study on CF for detecting stripe rust in wheat was conducted. The results showed that physiological parameters SPAD, photosynthetic rate decreased rapidly as leaf severity increases. CF parameters measured by modulated fluorometer showed that the maximal photochemical efficiency Fv/Fm and yield of quantum efficiency decreased gradually, whereas non-phochemical quenching co-effficient qN increased. CF intensity calculated from leaf apparent reflectance had an increase tendency at 685nm while decreased at 740nm. At the canopy level, CF at 688 nm was positively correlated with the disease index (DI) whereas CF at 760 nm was negatively correlated with DI. Ratios of CF at 688 to that at 760 nm, which found to be a suitable indicator of stress events in plants, were positively related to DI.5. The applicability of passive sensing of CF to the detection of crop stress was accessed. Spectral data and agricultural sampling data were not well linked together. On the basis of research on CF characteristics at leaf level, it is necessary to develop a model to simulate CF from leaf to canopy level, taking account of the influence of viewing geometry, atmospheric characteristics and the environmental factors. Additionally, CF technique should integrate with reflectance spectrum and crop cultivation characteristics in order to detect crop condition timely, rapidly and accurately, and to realize precision management under optimal regulation and control.更多还原