Comparison of total emitted solar-induced chlorophyll fluorescence (SIF) and top-of-canopy (TOC) SIF in estimating photosynthesis
Comparison of total emitted solar-induced chlorophyll fluorescence (SIF) and top-of-canopy (TOC) SIF in estimating photosynthesis
复制标题
总发射的太阳诱导叶绿素荧光 (SIF) 和冠层顶部 (TOC) SIF 在估计光合作用中的比较
DOI：
10.1016/j.rse.2020.112083
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发表时间：
2020
影响因子：
13.5
通讯作者：
Tang Jianwu
中科院分区：
文献类型：
--
作者：
Lu Xiaoliang;Liu Zhunqiao;Zhao Feng;Tang Jianwu
许多研究表明，太阳诱导荧光（SIF）在预测植被的初级生产总值（GPP）方面具有良好的潜力。我们通过遥感或近地表平台测量的是冠层顶部（TOC） SIF (SIFtoc)，由于（再）吸收和散射效应，它不一定等于或与整个冠层发射的总SIF （SIFtot）成比例。然而，光合作用，植物用来固定大气中碳的过程，发生在整个垂直树冠上。本文利用回忆理论，利用实测的SIFtoc、高光谱反射率(R)、冠层拦截(i)和叶片反照率（ωl）计算了760 nm处的SIFtoc总量。其中，两种sifto都可以通过同时测量TOC光谱得到；从开放获取的数据集中可以很好地估计出近红外区域的红外ω。我们的结果证实，测量的siftoly只占siftoly的一小部分：冠上传感器平均只能“看到”哈佛森林siftoly的22.9%。相对于sifto估计GPP， sifto有以下优势：(1) sifto改善了冠层GPP的日估算，尤其能够捕捉到可能导致其日差异较大的光合作用午间抑制；(2)对于冠层结构复杂或漫射光照较强的天空条件下的植物，sifto与GPP的相关性更强；(3)sifto -GPP关系对环境胁迫表现出更强的恢复能力。荧光逸出比（fesc），即siftoc乘以π与SIFtot之比，主要由太阳-冠层传感器的几何形状和叶片倾角分布决定。叶面积指数对叶片叶绿素浓度的影响在760 nm处呈边缘变化。我们的研究结果表明，将siftoc转换为siftoc可以更好地理解和估计GPP。
Many studies have shown that solar-induced fluorescence (SIF) has a good potential to predict gross primary production (GPP) of vegetation. What we measured by remote sensing or near-surface platforms is top-of-canopy (TOC) SIF (SIFtoc), which is not necessarily equal or proportional to total emitted SIF (SIFtot) from the entire canopy due to the (re)absorption and scattering effects. However, photosynthesis, the process that plants use to fix carbon from the atmosphere, occurs at the entire vertical canopy. Here, by using the recollision theory, we calculated SIFtotat 760 nm from the measured SIFtoc, hyperspectral reflectance (R), canopy interception (i) and leaf albedo (ωl). Among them, both SIFtocandRcan be obtained from concurrent TOC spectral measurements;iand ωlin the near-infrared region can be estimated from the open access datasets with a good accuracy. Our result confirms that the measured SIFtoconly accounts for a small fraction of SIFtot: the above-the-canopy sensor can only “see” on average 22.9% of SIFtotat Harvard Forest. SIFtothas the following advantages over SIFtocin estimating GPP: (1) SIFtotimproves the diurnal estimate of canopy GPP, especially capable to capture the midday depression of photosynthesis which may cause the large discrepancies between SIFtocand GPP on a diurnal basis, (2) SIFtotproduces a stronger correlation with GPP from plants with complex canopy structure or under sky conditions with more diffuse irradiance, and (3) the SIFtot-GPP relationship shows a stronger resilience to environmental stresses. The fluorescence escape ratio (fesc), the ratio between SIFtocmultiplied by π and SIFtot, is mostly determined by the sun-canopy-sensor geometry and leaf inclination distribution. The effect of LAI and the leaf chlorophyll concentration onfescis marginal at the 760 nm wavelength. Our results suggest that converting SIFtocinto SIFtotprovides a better tool to understand and estimate GPP.