Sensitivity Study of a Revised Leaf Photochemical Reflectance Index(PRI)
WU Chao-yang1,2,NIU Zheng1,TANG Quan1,2
1. The State Key Laboratory of Remote Sensing Science, Institute of Remote Sensing Applications, Chinese Academy of Sciences, Beijing 100101, China 2. Graduate School of Chinese Academy of Sciences, Beijing 100039, China
摘要： 光化学植被指数(PRI)被成功的应用于估算不同叶片生化组分的光能利用率(LUE)，这些生化组分包括叶片含水量、氮元素浓度等。以往的研究中已经成功建立了叶片、冠层和景观尺度PRI和LUE的相关关系。但是，为了利用PRI更加准确地估算叶片LUE，很多问题仍然亟需解决，比如当LUE高于0.03 mol CO2 mol-1 PPFD(photosynthetic photon flux density)，PRI会出现一个明显的饱和区域以及PRI和LUE关系会随季节发生较大变化。文章对PRI进行了修正，并基于PROSPECT模型对这一修正形式进行了4个参数的敏感性分析。分析结果表明，叶片SR-PRI(Simple ratio PRI) 对叶肉结构参数(N)、叶绿素浓度(cab)敏感性要高于叶片的等效水厚(cw) 和干物质浓度(cm)。因此叶肉结构参数(N) 和叶绿素浓度(cab)的微小变化都会造成SR-PRI的较大变化，进而影响到LUE的估算精度。对SR-PRI的实证实验表明，这一指数也能够很好地用来估算叶片的光能利用率并且结果要优于PRI和LUE之间的相关关系。SR-PRI最重要的一方面在于其更清晰的物理意义和对531 nm处反射率变化的敏感性，因为这一波段位置的反射率变化是评价光能利用率的核心参数。
关键词：光化学植被指数PRI;简单比值光化学植被指数SR-PRI;敏感性;修正
Abstract：Photochemical reflectance index (PRI) defined as a normalized difference index using two narrow reflectance bands at 531 and 570 nm that are closely related to xanthophyll cycle pigment content has been successfully used to estimate leaf photosynthetic light use efficiency (LUE) across species which vary in water content and nitrogen concentration. Previous research demonstrated that a consistent relationship could be established between PRI and LUE calculated from gas exchange measurements at the leaf, small canopy, and full forest or crop canopy scales. However, a number of problems, such as the saturation of PRI when LUE exceeds 0.03 mol CO2 mol-1PPED(photosynthetic photon flux density) and disjunctive relationships of PRI and LUE in seasonal changes, still existed and need to be handled in order to evaluate LUE more accurately. A sensitivity study of a revised PRI with four leaf parameters was performed based on PROSPECT model in the present article to study the effects of different biochemical concentrations on leaf SR-PRI (simple ratio PRI). Sensitivity study proved that leaf SR-PRI is more sensitive to leaf mesophyll structure parameter (N) and chlorophyll a+b content (cab) than parameters of dry matter content (cm) and equivalent water thickness (cw), indicating that leaf mesophyll structure parameter (N) and chlorophyll a+b content (cab) should be especially considered when acquiring leaf SR-PRI. And changes in the two parameters would cause large variation in SR-PRI which would reduce the precision for estimating light use efficiency. Validation study of SR-PRI was carried out in the analysis and the results proved that SR-PRI can also be a feasible index of estimating LUE for four species of plants with correlation coefficients better than that of PRI and LUE. The advantage of SR-PRI compared to PRI is its much clearer physical meaning and its sensitivity to the changes in reflectance at 531 nm which serves as a core parameter to evaluate light use efficiency.
Key words：Photochemical reflectance index (PRI);Simple ratio PRI (SR-PRI);Sensitivity;Revision
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