Inversion of net ecosystem CO2 flux measurements for estimation of canopy PAR absorption
Inversion of net ecosystem CO2 flux measurements for estimation of canopy PAR absorption
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DOI：
10.1046/j.1365-2486.2002.00488.x
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发表时间：
2002-06-01
影响因子：
11.6
通讯作者：
Walter-Shea, EA
中科院分区：
文献类型：
--
作者：
Hanan, NP;Burba, G;Walter-Shea, EA
光合有效辐射的分数吸收（f (PAR)）通常是描述陆地生态系统-大气相互作用、碳吸收、生长和生物地球化学的模型中的一个关键变量。我们提出了一种估算植物冠层光合成分吸收的入射光合有效辐射分数（f (Chl)）的新方法。该方法利用CO2通量和入射辐射的微气象测量来估计光响应参数，并由此推导出冠层结构。来自俄克拉何马州两个Ameriflux站点的数据，一个高草草原站点和一个小麦站点，被用来得出三年间（1997-1999）7天的移动平均估计f （Chl）。将反演估计值与PAR吸收的长期现场测量值进行比较。当田间测量的f （PAR）通过估计总叶面积的绿色部分来缩放时，获得了良好的相关性，尽管反向技术的值往往低于田间测量值。利用二氧化碳通量测量得到的f （Chl）的逆估计与其他更直接的技术可能得到的f （PAR）的测量不同。然而，由于反向估计值是基于观测到的冠层二氧化碳吸收量，它们可能被认为比受冠层非生理活性成分影响的直接测量更具生物学相关性。随着世界范围内涡动相关点数量的增加，该技术提供了检查单个点冠层结构和光收集能力的季节和年际变化的机会。此外，反演f （Chl）为开发和测试遥感反演f （PAR）提供了新的数据来源。因此，新的遥感算法，或对现有算法的调整，可能会比目前更好地适应“具有生物学意义的”光吸收。
The fractional absorption of photosynthetically active radiation (f (PAR) ) is frequently a key variable in models describing terrestrial ecosystem-atmosphere interactions, carbon uptake, growth and biogeochemistry. We present a novel approach to the estimation of the fraction of incident photosynthetically active radiation absorbed by the photosynthetic components of a plant canopy (f (Chl) ). The method uses micrometeorological measurements of CO2 flux and incident radiation to estimate light response parameters from which canopy structure is deduced. Data from two Ameriflux sites in Oklahoma, a tallgrass prairie site and a wheat site, are used to derive 7-day moving average estimates of f (Chl) during three years (1997-1999). The inverse estimates are compared to long-term field measurements of PAR absorption. Good correlations are obtained when the field-measured f (PAR) is scaled by an estimate of the green fraction of total leaf area, although the inverse technique tends to be lower in value than the field measurements.The inverse estimates of f (Chl) using CO2 flux measurements are different from measurements of f (PAR) that might be made by other, more direct, techniques. However, because the inverse estimates are based on observed canopy CO2 uptake, they might be considered more biologically relevant than direct measurements that are affected by non-physiologically active components of the canopy. With the increasing number of eddy covariance sites around the world the technique provides the opportunity to examine seasonal and inter-annual variation in canopy structure and light harvesting capacity at individual sites. Furthermore, the inverse f (Chl) provide a new source of data for development and testing of f (PAR) retrieval using remote sensing. New remote sensing algorithms, or adjustments to existing algorithms, might thus become better conditioned to 'biologically significant' light absorption than currently possible.