Unpacking the drivers of diurnal dynamics of sun-induced chlorophyll fluorescence (SIF): Canopy structure, plant physiology, instrument configuration and retrieval methods
Unpacking the drivers of diurnal dynamics of sun-induced chlorophyll fluorescence (SIF): Canopy structure, plant physiology, instrument configuration and retrieval methods
复制标题
DOI：
10.1016/j.rse.2021.112672
复制
发表时间：
2021-08-31
影响因子：
13.5
通讯作者：
Sun, Ying
中科院分区：
文献类型：
--
作者：
Chang, Christine Y.;Wen, Jiaming;Sun, Ying
来自星载传感器的太阳诱导叶绿素荧光 (SIF) 是全球碳循环监测的一种很有前途的工具，但其应用受到对昼夜 SIF 动态驱动因素了解不足的限制。来自地面塔的 SIF 测量可以揭示跨生物群落和环境条件的昼夜 SIF 动态；然而，对昼夜变化的有意义的解释需要理清冠层结构、植物生理学、仪器配置和检索方法的影响，这些影响常常相互作用并相互混淆。本研究的目的是使用 1）在玉米地同时进行地面和机载冠层尺度和叶片尺度测量来解开这些驱动因素，2）机械 SIF 模型，该模型明确考虑光化学（通过开放光系统 II 反应中心的分数，qL）和光保护（通过非光化学猝灭，NPQ）的动力学以及它们对子冠层光环境的交互依赖性，以及 3）SIF 仪器配置和检索方法的交叉比较。我们发现，在没有胁迫的情况下，作物行方向和太阳角度会导致 SIF 出现明显的中午下降，这是因为当作物行南北方向时，吸收的光合有效辐射 (APAR) 会在中午下降。冠层结构在垂直冠层内的不同位置引起 qL 和 NPQ 的独特响应，共同影响叶尺度的荧光量子产率 (Phi(F))。一旦在冠层尺度上整合，APAR 和冠层逃逸概率 (epsilon) 的昼夜动态对于准确塑造日间 SIF 变化至关重要。虽然叶级 qL 和 NPQ 表现出强烈的昼夜动态，但由于不同冠层对 SIF 的相反影响，它们的影响在冠层尺度上减弱。此外，不同的系统配置（即双半球形与半球形圆锥形）和检索方法可能会使 SIF 幅度产生偏差并扭曲其昼夜形状，因此混淆了对 SIF 发射的固有强度和动态的解释。我们的研究结果证明了作物行结构、冠层结构和植物生理学的交互变化、仪器配置和检索方法在形成昼夜 SIF 动态测量方面的重要性。这项研究强调了考虑这些因素以准确解释卫星 SIF 的必要性，并为未来跨站点使用不同 SIF 仪器和检索方法的综合工作提供信息。
Sun-induced chlorophyll fluorescence (SIF) from spaceborne sensors is a promising tool for global carbon cycle monitoring, but its application is constrained by insufficient understanding of the drivers underlying diurnal SIF dynamics. SIF measurements from ground-based towers can reveal diurnal SIF dynamics across biomes and environmental conditions; however, meaningful interpretation of diurnal variations requires disentangling impacts from canopy structure, plant physiology, instrument configuration and retrieval methods, which often interact with and confound each other. This study aims to unpack these drivers using 1) concurrent ground and airborne canopy-scale and leaf-scale measurements at a corn field, 2) a mechanistic SIF model that explicitly considers the dynamics of photochemistry (via the fraction of open photosystem II reaction centers, qL) and photoprotection (via nonphotochemical quenching, NPQ) as well as their interactive dependence on the sub canopy light environment, and 3) cross-comparison of SIF instrument configurations and retrieval methods. We found that crop row orientations and sun angles can introduce a distinctive midday dip in SIF in absence of stress, due to a midday drop of absorbed photosynthetically active radiation (APAR) when crop rows are north south oriented. Canopy structure caused distinctive responses in both qL and NPQ at different positions within the vertical canopy that collectively influenced fluorescence quantum yield (Phi(F)) at the leaf scale. Once integrated at the canopy scale, diurnal dynamics of both APAR and canopy escape probability (epsilon) are critical for accurately shaping diurnal SIF variations. While leaf-level qL and NPQ exhibited strong diurnal dynamics, their influence was attenuated at the canopy scale due to opposing effects on SIF at different canopy layers. Furthermore, different system configurations (i.e., bi-hemispherical vs. hemispherical-conical) and retrieval methods can bias the SIF magnitude and distort its diurnal shapes, therefore confounding the interpretation of inherent strength and dynamics of SIF emission. Our findings demonstrate the importance of crop row structures, interactive variations in canopy structure and plant physiology, instrument configuration, and retrieval method in shaping the measured dynamics of diurnal SIF. This study highlights the necessity to account for these factors to accurately interpret satellite SIF, and informs future synthesis work with different SIF instrumentation and retrieval methods across sites.