利用日光诱导叶绿素荧光监测水稻叶片叶绿素含量

    Monitoring of chlorophyll content in rice canopy and single leaf using sun-induced chlorophyll fluorescence

    • 摘要: 快速准确地监测作物叶片叶绿素含量对于研究作物光合作用、氮素营养以及胁迫状况至关重要。该研究基于不同品种、不同密度、不同氮素水平的水稻田间小区试验,分别获取冠层和单叶的辐亮度光谱、反射率光谱及生理生态指标等,计算日光诱导叶绿素荧光(Sun-Induced Chlorophyll Fluorescence,SIF)指数和植被指数,进一步基于线性回归和辐射传输模型2种方法来建立叶绿素含量监测模型,评估多个叶绿素监测模型的精度及适用性。结果表明:1)在冠层尺度,冠层761 nm处SIF强度(F761)与冠层叶绿素含量相关性最高,决定系数(Determination coefficient,R2)为0.72,略高于表现最好的红边叶绿素指数(Red edge Chlorophyll index,CIred edge)(R2=0.63);2)在单叶尺度,归一化下行SIF指数(↓FY NDFI)与单叶叶绿素含量相关性最高,R2为0.77,比表现最好的上行荧光产量双峰比值指数(↑FY687/↑FY741)R2高出0.10,与表现最好的植被指数CIred edge效果相当(R2=0.81);3)基于SCOPE(Soil Canopy Observation, Photochemistry and Energy fluxes )模型反演水稻冠层叶绿素含量的验证R2为0.57,均方根误差(Root Mean Squared Error,RMSE)为56.54 μg/cm,效果差于PROSAIL模型(模型检验的R2为0.91,RMSE为22.59 μg/cm);4)单叶Fluspect-B模型反演水稻单叶叶绿素含量的验证R2为0.55,均方根误差RMSE为19.45 μg/cm,效果差于PROCWT模型反演结果(R2为0.72,RMSE为6.42 μg/cm)。综上,SIF指数在监测冠层和单叶叶绿素含量时效果较好,基于SIF的辐射传输模型也可以用来反演水稻冠层和单叶的叶绿素含量。研究结果可为SIF监测作物叶绿素含量提供理论依据,并对未来利用SIF进行植物光合作用研究提供理论支持。

       

      Abstract: Abstract: Rapid and accurate monitoring leaf chlorophyll content is a critical step to explore the photosynthesis, nitrogen nutrition, and stress status of crops. Furthermore, vegetation index and radiation transfer model are widely used to determine the chlorophyll content in crops using the sun-induced chlorophyll fluorescence (SIF) technology. In this study, a monitoring model of chlorophyll content was established using linear regression and radiation transfer models, further to evaluate the accuracy and applicability for the rice growth and field management. A field plot test was carried out at the experimental base of National Engineering Technology Center for Information Agriculture (NETCIA) in Nantong City, Jiangsu Province, China. Different varieties of rice, densities and nitrogen application rates were set during test from May to October 2018. The radiance and reflectivity spectra of canopy and leaf scales were obtained using two hyperspectral spectrometers, thereby to calculate the chlorophyll content using Dualex instruments. Various SIF and vegetation indices were also calculated, where Fraunhofer line discrimination (FLD) was utilized to extract the canopy fluorescence intensities at 687 and 761 nm. A chlorophyll content model was then constructed using the canopy SIF intensity and leaf SIF index, where a reflectivity vegetation index was utilized to compare with the predicted one. A look-up table was also prepared for the inversion of rice canopy and leaf chlorophyll content using the SCOPE and Fluspect-B models. PROSAIL and PROCWT models were also selected to assess the hyperspectral reflectance inversion. Root mean square error (RMSE) and determination coefficient (R2) were used to evaluate the accuracy of chlorophyll content inversion. The results showed that: 1) The canopy SIF intensity F761 presented the strongest correlation with the canopy chlorophyll content (R2 = 0.72), better than the red edge chlorophyll index (CI red edge, R2=0.63); 2) The downward SIF index at the leaf scale behaved the strongest correlation (R2= 0.77) with the leaf chlorophyll content, compared with the upward SIF index, similar to the best performing vegetation index CIred edge (R2=0.81). 3) The PROSAIL model was used for the inversion of canopy chlorophyll content (R2 = 0.91, RMSE = 22.59 μg/cm), better than the SCOPE model (R2 =0.57, RMSE = 56.54 μg/cm); 4) The PROCWT model was used for the inversion of leaf chlorophyll content (R2 = 0.72, RMSE = 6.42 μg/cm), better than the Fluspect-B model (R2 = 0.55, RMSE = 19.45 μg/cm). Consequently, the SIF index demonstrated a better performance on the chlorophyll content at canopy and leaf scales. An excellent feasibility was also found in the radiation transport model using SIF to invert the chlorophyll content. The findings can provide a promising theoretical support to monitor the crop chlorophyll content for plant photosynthesis using SIF in the future. The next step can be recommended to maximize the number of test samples for a higher inversion accuracy of Fluspect-B and SCOPE radiation transfer models.

       

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