Brissette Logan E G, Wong Christopher Y S, McHugh Devin P, Au Jessie, Orcutt Erica L, Klein Marie C, Magney Troy S
Department of Plant Sciences, University of California, Davis, Davis, CA 95616, USA.
Department of Geography, California State University, Sacramento, Sacramento, CA 95819, USA.
AoB Plants. 2023 Oct 18;15(5):plad069. doi: 10.1093/aobpla/plad069. eCollection 2023 Oct.
Chlorophyll fluorescence measured at the leaf scale through pulse amplitude modulation (PAM) has provided valuable insight into photosynthesis. At the canopy- and satellite-scale, solar-induced fluorescence (SIF) provides a method to estimate the photosynthetic activity of plants across spatiotemporal scales. However, retrieving SIF signal remotely requires instruments with high spectral resolution, making it difficult and often expensive to measure canopy-level steady-state chlorophyll fluorescence under natural sunlight. Considering this, we built a novel low-cost photodiode system that retrieves far-red chlorophyll fluorescence emission induced by a blue light emitting diode (LED) light source, for 2 h at night, above the canopy. Our objective was to determine if an active remote sensing-based night-time photodiode method could track changes in canopy-scale LED-induced chlorophyll fluorescence (LEDIF) during an imposed drought on a broadleaf evergreen shrub, . Far-red LEDIF (720-740 nm) was retrieved using low-cost photodiodes (LEDIF) and validated against measurements from a hyperspectral spectroradiometer (LEDIF). To link the LEDIF signal with physiological drought response, we tracked stomatal conductance () using a porometer, two leaf-level vegetation indices-photochemical reflectance index and normalized difference vegetation index-to represent xanthophyll and chlorophyll pigment dynamics, respectively, and a PAM fluorimeter to measure photochemical and non-photochemical dynamics. Our results demonstrate a similar performance between the photodiode and hyperspectral retrievals of LEDIF ( = 0.77). Furthermore, LEDIF closely tracked drought responses associated with a decrease in photochemical quenching ( = 0.69), / ( = 0.59) and leaf-level photochemical reflectance index ( = 0.59). Therefore, the low-cost LEDIF approach has the potential to be a meaningful indicator of photosynthetic activity at spatial scales greater than an individual leaf and over time.
通过脉冲幅度调制（PAM）在叶片尺度上测量叶绿素荧光，为光合作用提供了有价值的见解。在冠层和卫星尺度上，太阳诱导荧光（SIF）提供了一种跨时空尺度估算植物光合活性的方法。然而，远程获取SIF信号需要具有高光谱分辨率的仪器，这使得在自然阳光下测量冠层水平的稳态叶绿素荧光既困难又往往成本高昂。考虑到这一点，我们构建了一种新型低成本光电二极管系统，该系统在夜间冠层上方2小时内，获取由蓝光发光二极管（LED）光源诱导的远红光叶绿素荧光发射。我们的目标是确定基于主动遥感的夜间光电二极管方法是否能够跟踪阔叶常绿灌木在遭受干旱期间冠层尺度LED诱导叶绿素荧光（LEDIF）的变化。使用低成本光电二极管（LEDIF）获取远红光LEDIF（720 - 740纳米），并与高光谱分光辐射计的测量结果（LEDIF）进行验证。为了将LEDIF信号与生理干旱响应联系起来，我们使用气孔计跟踪气孔导度（），使用两个叶片水平植被指数——光化学反射指数和归一化差异植被指数，分别代表叶黄素和叶绿素色素动态，并用PAM荧光计测量光化学和非光化学动态。我们的结果表明，光电二极管和高光谱对LEDIF的反演具有相似的性能（ = 0.77）。此外，LEDIF紧密跟踪了与光化学猝灭降低（ = 0.69）、 / （ = 0.59）和叶片水平光化学反射指数（ = 0.59）相关的干旱响应。因此，低成本的LEDIF方法有可能成为大于单叶空间尺度且随时间变化的光合活性的有意义指标。
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