Solar-induced chlorophyll fluorescence (SIF) observed by satellites has advanced the monitoring of terrestrial photosynthesis regionally and globally. The relationship between SIF and gross primary production (GPP) at leaf, canopy, and ecosystem scales has received tremendous attention in recent years. It remains controversial whether the SIF-GPP relationship at the ecosystem scale is universal or dependent upon vegetation type. New SIF observations from the TROPOspheric Monitoring Instrument (TROPOMI) with unprecedented high spatial and temporal resolution provide a new opportunity to elucidate the SIF-GPP relationship. Here, we examine the SIF-GPP relationship for seven major vegetation types across the U.S. with TROPOMI SIF and in-situ GPP data for 83 eddy covariance flux sites. We find that TROPOMI SIF shows a strong and consistent relationship with tower-based GPP at both satellite footprint and grid-cell levels. The slope of the SIF-GPP relationship is similar among all the vegetation types except croplands, demonstrating a nearly universal (converging to ~13.5 g C m⁻² d⁻¹/W m⁻² μm⁻¹ sr⁻¹) rather than vegetation type-specific SIF-GPP relationship. This confirms that TROPOMI SIF can be used as a proxy for GPP across a wide variety of vegetation types, and can also be used to quantify GPP by avoiding uncertainty associated with land cover maps. The C₄ crops have a much higher slope than the C₃ crops, and therefore croplands tend to have a higher slope than C₃-dominated vegetation types (e.g., forests, shrublands, savannas). We also find that the TROPOMI SIF is well correlated with GPP under normal or wetter conditions, while their relationship becomes weaker under water stress. Our TROPOMI-based study could improve our understanding of the SIF-GPP relationship at the ecosystem scale and advance the mapping of GPP globally with SIF observations from space.

卫星观测到的太阳诱导叶绿素荧光 (SIF) 促进了区域和全球陆地光合作用的监测。近年来，SIF 与叶、冠层和生态系统尺度的初级生产总值 (GPP) 之间的关系受到了极大的关注。生态系统尺度上的 SIF-GPP 关系是普遍存在的还是依赖于植被类型仍然存在争议。来自对流层监测仪器 (TROPOMI) 的新 SIF 观测具有前所未有的高时空分辨率，为阐明 SIF-GPP 关系提供了新的机会。在这里，我们使用 TROPOMI SIF 和 83 个涡流协方差通量站点的原位 GPP 数据检查了美国七种主要植被类型的 SIF-GPP 关系。我们发现 TROPOMI SIF 在卫星足迹和网格单元级别都与基于塔的 GPP 显示出强烈且一致的关系。SIF-GPP 关系的斜率在除农田之外的所有植被类型中都相似，表明几乎普遍（收敛到 ~13.5 g C m^-2 d ^-1 /W m ^-2  μ m ^-1  sr ^-1 ) 而不是特定于植被类型的 SIF-GPP 关系。这证实了 TROPOMI SIF 可用作各种植被类型的 GPP 的代理，也可用于通过避免与土地覆盖图相关的不确定性来量化 GPP。C ₄作物的坡度远高于 C ₃作物，因此农田的坡度往往高于 C ₃- 主导的植被类型（例如，森林、灌木地、稀树草原）。我们还发现 TROPOMI SIF 在正常或潮湿条件下与 GPP 有很好的相关性，而在水分胁迫下它们的关系变弱。我们基于 TROPOMI 的研究可以提高我们对生态系统尺度上 SIF-GPP 关系的理解，并通过 SIF 空间观测推进全球 GPP 制图。