Ground solar-induced chlorophyll fluorescence (SIF) is important for the mechanistic understanding of the dynamics of vegetation gross primary production (GPP) at fine spatiotemporal scales. However, eddy covariance (EC) observations generally cover larger footprint areas than ground SIF observations (a bare fiber with nadir), and this footprint mismatch between nadir SIF and GPP could complicate the canopy SIF-GPP relationships. Here, we upscaled nadir SIF observations to EC footprint and investigated the change in SIF-GPP relationships after the upscaling in cropland. We included 13 site-years data in our study, with seven site-years corn, four site-years soybeans, and two site-years miscanthus, all located in the US Corn Belt. All sites’ crop nadir SIF observations collected from the automated FluoSpec2 system (a hemispheric-nadir system) were upscaled to the GPP footprint-based SIF using vegetation indices (VIs) calculated from high spatiotemporal satellite reflectance data. We found that SIF-GPP relationships were not substantially changed after upscaling nadir SIF to GPP footprint at our crop sites planted with corn, soybean, and miscanthus, with R² change after the upscaling ranging from -0.007 to 0.051 and root mean square error (RMSE) difference from -0.658 to 0.095 umol m ^− 2 s ^− 1 relative to original nadir SIF-GPP relationships across all the site-years. The variation of the SIF-GPP relationship within each species across different site-years was similar between the original nadir SIF and upscaled SIF. Different VIs, EC footprint models, and satellite data led to marginal differences in the SIF-GPP relationships when upscaling nadir SIF to EC footprint. Our study provided a methodological framework to correct this spatial mismatch between ground nadir SIF and GPP observations for croplands and potentially for other ecosystems. Our results also demonstrated that the spatial mismatch between ground nadir SIF and GPP might not significantly affect the SIF-GPP relationship in cropland that are largely homogeneous.

地面太阳诱导的叶绿素荧光 (SIF) 对于精细时空尺度上植被总初级生产 (GPP) 动态的机制理解很重要。然而，涡度协方差 (EC) 观测通常覆盖比地面 SIF 观测（带最低点的裸纤维）更大的足迹区域，并且最低点 SIF 和 GPP 之间的这种足迹不匹配可能会使冠层 SIF-GPP 关系复杂化。在这里，我们将最低点 SIF 观测值升级为 EC 足迹，并研究了农田升级后 SIF-GPP 关系的变化。我们在研究中纳入了 13 个站点年的数据，其中七个站点年的玉米、四个站点年的大豆和两个站点年的芒草均位于美国玉米带。使用从高时空卫星反射率数据计算的植被指数 (VI)，将从自动化 FluoSpec2 系统（半球-最低点系统）收集的所有站点的作物最低点 SIF 观测值升级为基于 GPP 足迹的 SIF。我们发现，在我们种植玉米、大豆和芒草的作物地点将最低点 SIF 升级到 GPP 足迹后，SIF-GPP 关系没有实质性改变，其中 R²放大后的变化范围从 -0.007 到 0.051，均方根误差 (RMSE) 差异从 -0.658 到 0.095 umol m  ^{−  2} s  ^{−  1}相对于所有站点年的原始最低点 SIF-GPP 关系。每个物种在不同地点年内的 SIF-GPP 关系的变化在原始最低点 SIF 和升级后的 SIF 之间是相似的。当将最低点 SIF 升级到 EC 足迹时，不同的 VI、EC 足迹模型和卫星数据导致 SIF-GPP 关系的边际差异。我们的研究提供了一个方法框架来纠正地面最低点 SIF 和 GPP 对农田和潜在的其他生态系统的观测之间的空间不匹配。我们的结果还表明，地面最低点 SIF 和 GPP 之间的空间不匹配可能不会显着影响在很大程度上同质的农田中的 SIF-GPP 关系。