Solar-induced Fluorescence (SIF) has an advantage over greenness-based Vegetation Indices in detecting drought. This advantage is the mechanistic coupling between SIF and Gross Primary Productivity (GPP). Under water stress, SIF tends to decrease with photosynthesis, due to an increase in non-photochemical quenching (NPQ), resulting in rapid and/or sustained reductions in the fluorescence quantum efficiency (Φ_F). Water stress also affects vegetation structure via highly dynamic changes in leaf angular distributions (LAD) or slower changes in leaf area index (LAI). Critically, these responses are entangled in space and time and their relative contribution to SIF, or to the coupling between SIF and GPP, is unclear. In this study, we quantify the relative effect of structural and photosynthetic dynamics on the diurnal and spatial variation of canopy SIF in a potato crop in response to a replicated paired-plot water stress experiment. We measured SIF using two platforms: a hydraulic lift and an Unmanned Aerial Vehicle (UAV) to capture temporal and spatial variation, respectively. LAD parameters were estimated from point clouds and photographic data and used to assess structural dynamics. Leaf Φ_F estimated from PAM fluorescence measurements were used to represent variations in photosynthetic regulation. We also measured foliar pigments, operating quantum yield of photosystem II (PSII), photosynthetic gas exchange, stomatal conductance and LAI. We used a radiative transfer model (SCOPE) to provide a means of decoupling structural and photosynthetic factors across the diurnal and spatial domains. The results demonstrate that diurnal variation in SIF is driven by photosynthetic and structural dynamics. The influence of Φ_F was prominent in the diurnal SIF response to water stress, with reduced fluorescence efficiencies in stressed plants. Structural factors dominated the spatial response of SIF to water stress over and above Φ_F. The results showed that the relationship between SIF and GPP is maintained in response to water stress where adjustments in NPQ and leaf angle co-operate to enhance the correlation between SIF and GPP. This study points to the complexity of interpreting and modelling the spatiotemporal connection between SIF and GPP which requires simultaneous knowledge of vegetation structural and photosynthetic dynamics.

太阳诱导荧光 (SIF) 在检测干旱方面优于基于绿度的植被指数。这种优势是 SIF 和总初级生产力 (GPP) 之间的机械耦合。在水分胁迫下，由于非光化学猝灭 (NPQ) 的增加，SIF 往往随着光合作用而降低，导致荧光量子效率 (Φ _F ) 快速和/或持续降低）。水分胁迫还通过叶角分布 (LAD) 的高度动态变化或叶面积指数 (LAI) 的较慢变化来影响植被结构。至关重要的是，这些响应在空间和时间上纠缠不清，它们对 SIF 或 SIF 与 GPP 之间的耦合的相对贡献尚不清楚。在这项研究中，我们量化了结构和光合动力学对马铃薯作物冠层 SIF 日变化和空间变化的相对影响，以响应重复的配对小区水分胁迫实验。我们使用两个平台测量 SIF：液压升降机和无人机 (UAV)，分别捕捉时间和空间变化。LAD 参数是根据点云和摄影数据估计的，并用于评估结构动力学。叶Φ _F从 PAM 荧光测量估计值被用来表示光合作用调节的变化。我们还测量了叶色素、光系统 II (PSII) 的操作量子产率、光合气体交换、气孔导度和 LAI。我们使用辐射传输模型 (SCOPE) 提供了一种在昼夜和空间域中分离结构和光合因素的方法。结果表明，SIF 的昼夜变化是由光合作用和结构动力学驱动的。Φ _F的影响在昼夜 SIF 对水分胁迫的响应中表现突出，胁迫植物的荧光效率降低。结构因素主导了 SIF 对超过 Φ _{F 的}水分胁迫的空间响应. 结果表明，SIF 和 GPP 之间的关系在响应水分胁迫时得以保持，其中 NPQ 和叶角的调整协同增强了 SIF 和 GPP 之间的相关性。这项研究指出了解释和建模 SIF 和 GPP 之间时空联系的复杂性，这需要同时了解植被结构和光合动力学。