Abstract Plant functional traits such as photosynthetic capacity are critical parameters for terrestrial biosphere models. However, their spatial and temporal characteristics are still poorly represented. In this study, we used satellite observations of sun-induced fluorescence (SIF) to estimate top-of-canopy photosynthetic capacity (maximum carboxylation rate, Vcmax at a reference temperature of 25 °C) for crops, which was in turn utilized to simulate regional gross primary production (GPP). We first estimate the key parameter, Vcmax, in the widely-used FvCB photosynthesis model using field measurements of CO2 and water fluxes during 2007–2012 at seven crop eddy covariance flux sites over the US Corn Belt. The results showed that satellite far-red SIF retrievals have a stronger link to Vcmax at the seasonal scale (R2 = 0.70 for C4 and R2 = 0.63 for C3 crop) as compared with widely-used vegetation indices. We calibrate an empirical model linking Vcmax with SIF that was used to estimate spatially and temporally varying crop Vcmax for the US Corn Belt region. The resulting Vcmax maps are used together with meteorological data from MERRA reanalysis data and vegetation structural parameters derived from the satellite-based spectral reflectance data to constrain the Soil-Canopy Observation of Photosynthesis and Energy (SCOPE) balance model in order to estimate regional crop GPP. Our results show a substantial improvement in the seasonal and spatial patterns of cropland GPP when compared with crop yield inventory data. The evaluation with tall tower atmospheric CO2 measurements further supports our estimation of spatiotemporal Vcmax from space-borne SIF. Considering that SIF has a direct link to photosynthetic activity, our findings highlight the potential to infer regional Vcmax using remotely sensed SIF data and to use this information for a better quantification of regional cropland carbon cycles.

中文翻译：

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通过使用天基叶绿素荧光数据对作物光合能力进行空间明确监测

摘要 植物功能性状如光合能力是陆地生物圈模型的关键参数。然而，它们的空间和时间特征仍然没有得到很好的体现。在这项研究中，我们使用太阳诱导荧光 (SIF) 的卫星观测来估计作物的冠层光合能力（最大羧化率，参考温度为 25 °C 时的 Vcmax），进而用于模拟区域初级生产总值（GPP）。我们首先使用 2007-2012 年期间美国玉米带上七个作物涡流协方差通量站点的 CO2 和水通量的现场测量来估计广泛使用的 FvCB 光合作用模型中的关键参数 Vcmax。结果表明，卫星远红 SIF 反演在季节性尺度上与 Vcmax 有更强的联系（C4 的 R2 = 0.70，R2 = 0。63 C3 作物）与广泛使用的植被指数相比。我们校准了一个将 Vcmax 与 SIF 联系起来的经验模型，该模型用于估计美国玉米带地区随空间和时间变化的作物 Vcmax。得到的 Vcmax 地图与来自 MERRA 再分析数据的气象数据和来自卫星光谱反射率数据的植被结构参数一起使用，以约束光合作用和能量的土壤-冠层观测 (SCOPE) 平衡模型，以估计区域作物 GPP . 我们的结果表明，与作物产量清单数据相比，农田 GPP 的季节性和空间格局有了显着改善。对高塔大气 CO2 测量的评估进一步支持我们从星载 SIF 估计时空 Vcmax。