湿地植被叶面积指数对光化学指数和光能利用率关系的影响————基于实测数据和PROSPECT-SAIL模型

光化学指数PRI(Photochemical Reflectance Index)是估算光能利用率LUE(Light Use Efficiency)的一种快速监测的有效指标,分析各种因素对二者的影响是提高估算精度的前提.论文针对三种杭州湾典型湿地植物 [旱柳(Salix matsudana),柽柳(Tamarix chinensis)和芦苇(Phragm itescommunis)],实地观测了其光合作用及日变化,叶面积指数以及同步植被光谱.同时采用PROSPECT-SAIL模型模拟叶面积指数LAI(Leaf Area Index)从小到大变化时植被冠层反射率,分析LAI的变化对冠层PRI的影响.结果表明:1)三种植被在日变化上,芦苇,旱柳和柽柳的PRI和LUE的相关性较好,R²分别为0.581 6,0.524 6和0.514 6;而对同一种植被在不考虑时间变化的条件下,PRI和LUE的相关性会有所减弱,对于LAI较小的冠层,PRI不能精确反映LUE;2)当LAI < 5时,冠层下土壤背景对冠层PRI影响较大,在不同土壤背景下,土壤亮度低的对冠层PRI影响较小;3)当LAI > 5时,土壤背景对冠层PRI影响较小,冠层自身的LAI才是影响PRI和LUE相关性的决定因素.因此,PRI和LUE关系模型还需要进一步探索和完善,引入更精确的模型和参数,不断提高LUE估算的准确度.

Research on the Effect of Wetland Vegetation LAI on the Relationship between LUE and PRI by in situ Data and PROSPECT-SAIL Model

Photochemical Reflectance Index (PRI) is an effective index to rapidly estimate Light Use Efficiency (LUE). The analysis of various factors influencing the relationship between these two variables is the premise for improving the precision of estimating LUE. In this paper, three kinds of wetland plants Salix matsudana, Tamarix chinensis and Phragm itescommunis in Hangzhou Bay were selected, and the diurnal variations of their photosynthesis and the synchronous vegetation spectrum were measured. At the same time, the PROSPECT-SAIL model was used to simulate the Leaf Area Index (LAI) of canopies from small to large vegetation, and the effect of LAI on the relationship between canopy PRI and LUE were analyzed. The results showed that: 1) the diurnal variations of PRI and LUE all have good relations for Phragm itescommunis, Salix matsudana and Tamarix chinensis, and the R² were 0.581 6, 0.524 6 and 0.514 6, respectively; however the correlation between PRI and LUE of the same vegetation in different periods of growth will be weakened, since PRI can't accurately estimate the LUE when the canopy LAI is small. 2) When LAI < 5, the soil background has great influence on canopy PRI, and the low brightness of soil has less affected on the canopy PRI. 3) When LAI > 5, the soil background has little influence on canopy PRI, and canopy LAI itself is the key factor that influence the relationships between PRI and LUE. Therefore, the relationships between PRI and LUE needs further exploration, such as model improving and more parameters should be researched in order to constantly improve the accuracy of the LUE estimation.