资源与生态学报

资源与生态学报 ›› 2020, Vol. 11 ›› Issue (3): 253-262.DOI: 10.5814/j.issn.1674-764X.2020.03.002

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Tibet西藏高寒草甸冠层光合参数的遥感估算：站点研究

牛犇1, 何永涛1,2, 张宪洲1,2,*(), 石培礼1,2, 杜明远3   

  1. 1. 中国科学院地理科学与资源研究所,生态系统网络观测与模拟重点实验室,拉萨高原生态研究中心,北京 100101
    2. 中国科学院大学,资源与环境学院,北京 100190
    3. 日本国家农业环境科学研究所, 农业和粮食研究组,筑波 305-8604,日本
  • 收稿日期:2020-03-02 接受日期:2020-04-11 出版日期:2020-05-30 发布日期:2020-06-16
  • 通讯作者: 张宪洲

Satellite-based Estimates of Canopy Photosynthetic Parameters for an Alpine Meadow in Northern

NIU Ben1, HE Yongtao1,2, ZHANG Xianzhou1,2,*(), SHI Peili1,2, DU Mingyuan3   

  1. 1. Lhasa Plateau Ecosystem Research Station, Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China
    2. College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100190, China
    3. Institute for Agro-Environmental Sciences, National Agriculture and Food Research Organization, Ibaraki 305-8604, Japan
  • Received:2020-03-02 Accepted:2020-04-11 Online:2020-05-30 Published:2020-06-16
  • Contact: ZHANG Xianzhou
  • About author:NIU Ben, E-mail: niub@igsnrr.ac.cn
  • Supported by:
    The National Key Research and Development Program of China(2016YFC0502001);The National Natural Science Foundation of China(41807331);The West Light Foundation of the Chinese Academy of Sciences(2018)

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摘要：

太阳辐射驱动的植物光合作用是所有生物圈功能的基础。高寒草甸生态系统范围广,土壤碳密度高,气候变化剧烈,因此是高寒生态系统关键过程响应气候变化的指示器。然而,对高寒草甸生态系统光合作用的主要参数,包括被冠层吸收的光合有效辐射占比（FPAR）、冠层消光系数（k）和冠层叶面积指数（LAI）季节动态的研究较为缺乏。利用2009-2011年太阳辐射各组分和植被叶面积指数观测,分别估算了位于西藏自治区当雄县一个典型的高寒草地生态系统的这三个光合参数,并与最新MODIS（collection 6）遥感FPAR（FPAR_MOD）和LAI产品（LAI_MOD）进行了对比。此外,基于比尔-朗伯吸收定律和MODIS植被指数产品（归一化植被指数NDVI和增强型植被指数EVI）,本研究介绍了一个纯遥感手段估算高寒草甸生态系统植被冠层光合参数季节动态的方法。结果表明：2009-2011年该研究区高寒草甸日均FPAR分别是0.33、0.37和0.35,所有4个基于遥感的FPAR产品,包括FPAR_MOD、基于比尔-朗伯吸收定律（常数化消光系数为0.5）估算的FPAR_LAI,以及2个利用MODIS植被指数产品与FPAR地面观测（FAPRg）建立非线性统计模型估算的FPAR（FPAR_NDVI和FPAR_EVI）均对FPARg的年内季节变异做出了很好的解释。相比而言,FPAR_MOD严重低估了FPARg,低估量超过了FPARg本身的40%;FPAR_LAI也明显低估了FPARg,低估量将近 20%,这主要是由于比尔-朗伯吸收定律中k值在整个生长季都被设置为常数0.5,因此用FPAR_LAI去校准FPAR_MOD在该高寒草甸不是一个科学合理的方法。通过遥感估算,该高寒草甸的k值存在明显的季节变异,变异范围是0.19-2.95。考虑k值的季节变化后,FPAR_NDVI和FPAR_EVI明显地提高了对FPARg的估算精度,二者对FPARg虽然有轻微的高估,但高估量均不到5%（RMSE=0.05）。基于植被指数（NDVI和EVI）模拟的FPAR和k的季节动态,利用比尔-朗伯吸收定律估算的植被叶面积指数（LAI_NDVI和LAI_EVI）明显提高了遥感LAI_MOD产品的准确度。本研究揭示了基于比尔-朗伯吸收定律,植被指数构建的遥感模型可以提供该高寒草甸FPAR、k和LAI季节动态简单而有效的估算方法。

关键词: 太阳辐射组分, 比尔-朗伯吸收定律, 消光系数, 叶面积指数, 高寒草甸, 西藏高原

Abstract:

Plant photosynthesis is the fundamental driver of all the biospheric functions. Alpine meadow on the Tibetan Plateau is sensitive to rapid climate change, and thus can be considered an indicator for the response of terrestrial ecosystems to climate change. However, seasonal variations in photosynthetic parameters, including the fraction of photosynthetically active radiation by canopy (FPAR), the light extinction coefficient (k) through canopy, and the leaf area index (LAI) of plant communities, are not known for alpine meadows on the Tibetan Plateau. In this study, we used field measurements of radiation components and canopy structure from 2009 to 2011 at a typical alpine meadow on the northern Tibetan Plateau to calculate these three photosynthetic parameters. We developed a satellite-based (NDVI and EVI) method derived from the Beer-Lambert law to estimate the seasonal dynamics of FPAR, k ,and LAI, and we compared these estimates with the Moderate Resolution Imaging Spectroradiometer (MODIS) FPAR (FPAR_MOD) and LAI product (LAI_MOD). The results showed that the average daily FPAR was 0.33, 0.37 and 0.35, respectively, from 2009 to 2011, and that the temporal variations could be explained by all four satellite-based FPAR estimations, including FPAR_MOD, an FPAR estimation derived from the Beer-Lambert law with a constant k (FPAR_LAI), and two FPAR estimations from the nonlinear functions between the ground measurements of FPAR (FAPRg) and NDVI/EVI (FPAR_NDVI and FPAR_EVI). We found that FPAR_MOD seriously undervalued FPARg by over 40%. Tower-based FPAR_LAI also significantly underestimated FPARg by approximately 20% due to the constant k (0.5) throughout the whole growing seasons. This indicated that using FPAR_LAI to validate the FPAR_MOD was not an appropriate method in this alpine meadow because the seasonal variation of k ranged from 0.19 to 2.95 in this alpine meadow. Thus, if the seasonal variation of k was taken into consideration, both FPAR_NDVI and FPAR_EVI provided better descriptions, with negligible overestimates of less than 5% of FAPRg (RMSE=0.05), in FPARg estimations than FPAR_MOD and FPAR_LAI. Combining the satellite-based (NDVI and EVI) estimations of seasonal FPAR and k, LAI_NDVI and LAI_EVI derived from the Beer-Lambert law also provided better LAIg estimations than LAI_MOD (less than 30% of LAIg). Therefore, this study concluded that satellite-based models derived from the Beer-Lambert law were a simple and efficient method for estimating the seasonal dynamics of FPAR, k and LAI in this alpine meadow.

Key words: radiation components, Beer-Lambert law, light extinction coefficient, leaf area index, alpine meadow, Tibetan Plateau