Spatially and temporally continuous estimation of plant photosynthetic carbon fixation (or gross primary production, GPP) is crucial to our understanding of the global carbon cycle and the impact of climate change. Besides spatial, seasonal and interannual variations, GPP also exhibits strong diurnal variations. Satellite retrieved solar-induced chlorophyll fluorescence (SIF) provides a spatially continuous, but temporally discrete measurement of plant photosynthesis, and has the potential to be used to estimate GPP at global scale. However, it remains unclear whether the seasonal time series of SIF snapshots taken at a fixed time of the day can be used to infer daily total GPP variation at spatial and seasonal scales. In this study, we first used GPP estimates from 135 eddy covariance flux sites, covering a wide range of geographic locations and biome types, to investigate the relationship between the instantaneous GPP (GPPinst) and daily GPP (GPPdaily) on the seasonal course for different times of the day. Latitudinal and diurnal patterns were found to correspond to variations in photosynthetically active radiation (PAR) and light use efficiency (LUE), respectively. We then used the Soil-Canopy Observation Photosynthesis and Energy Balance (SCOPE) model and the FluxCom GPP product to investigate the instantaneous and daily SIF-GPP relationships at five flux tower sites along a latitudinal gradient and at a global scale for different biome types. The results showed that daily SIF had a stronger linear correlation with daily GPP than instantaneous SIF at the seasonal scale, with an instantaneous to daily SIF conversion factor following the latitudinal and seasonal pattern driven by PAR. Our study highlights the necessity to take the latitudinal and diurnal factors into consideration for SIF-GPP relationship analyses or for physiological phenology analyses based on SIF.

中文翻译：

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关于次日瞬时和每日总初级生产总值之间的关系：对解释基于卫星的 SIF 反演的影响

植物光合碳固定（或初级生产总值，GPP）的空间和时间连续估计对于我们理解全球碳循环和气候变化的影响至关重要。除了空间、季节和年际变化，GPP 还表现出强烈的日变化。卫星回收的太阳诱导叶绿素荧光 (SIF) 提供了植物光合作用的空间连续但时间离散的测量，并有可能用于估计全球范围内的 GPP。然而，目前尚不清楚在一天中固定时间拍摄的 SIF 快照的季节性时间序列是否可用于推断空间和季节性尺度上的每日总 GPP 变化。在这项研究中，我们首先使用了来自 135 个涡流协方差通量站点的 GPP 估计值，涵盖广泛的地理位置和生物群落类型，以研究一天中不同时间季节性课程的瞬时 GPP (GPPinst) 和每日 GPP (GPPdaily) 之间的关系。发现纬度和昼夜模式分别对应于光合有效辐射 (PAR) 和光利用效率 (LUE) 的变化。然后，我们使用土壤冠层观测光合作用和能量平衡 (SCOPE) 模型和 FluxCom GPP 产品来研究沿纬度梯度和全球范围内不同生物群落类型的五个通量塔站点的瞬时和每日 SIF-GPP 关系。结果表明，在季节性尺度上，日 SIF 与日 GPP 的线性相关性强于瞬时 SIF，具有遵循 PAR 驱动的纬度和季节模式的瞬时到每日 SIF 转换因子。我们的研究强调了在 SIF-GPP 关系分析或基于 SIF 的生理物候分析中考虑纬度和昼夜因素的必要性。