Diffuse radiation can increase the light use efficiency for plant photosynthesis. However, the lack of observations limits the explorations of diffuse fertilization effects on the global scale. Here, we bias-correct global hourly diffuse fraction (K_d) from a climate reanalysis using an artificial neural network (ANN) model in combination with site-level observations. Evaluations at independent sites show that the updated K_d on average increases correlations by 9.7% and reduces root-mean-square errors (RMSEs) by 45.5% against measurements than the original reanalysis. The derived radiative fluxes are then used as input for a dynamic vegetation model to explore the impacts of diffuse radiation on global gross primary productivity (GPP) during 1981–2015. With the updated K_d, simulated GPP shows lower RMSEs against observations at 72 out of 76 FLUXNET sites, leading to a reduced RMSE of 9.9% on average. Moreover, simulations with updated K_d present higher global GPP (3.1%) than that with original K_d from Modern-Era Retrospective Analysis for Research and Applications (MERRA) product. The simulations show that diffuse radiation, which accounts for 54% of the total shortwave radiation, contributes to long-term global mean GPP by 1.49 g C m⁻² day⁻¹ (64.3%). During 1981–2015, the changes of direct radiation result in a global GPP trend of −0.49 g C m⁻² yr⁻², which is offset by 0.31 g C m⁻² yr⁻² (53.1%) following the enhancement of diffuse radiation.

中文翻译：

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1981-2015 年漫辐射对全球初级生产力的巨大贡献

漫辐射可以提高植物光合作用的光利用效率。然而，缺乏观察限制了对全球范围内扩散施肥效应的探索。在这里，我们使用人工神经网络 (ANN) 模型结合站点级观测，从气候再分析中对全球每小时扩散分数 ( K _d ) 进行偏差校正。独立站点的评估表明，更新后的K _d与原始再分析相比，平均而言，相关性提高了 9.7%，并且相对于测量的均方根误差 (RMSE) 降低了 45.5%。然后将导出的辐射通量用作动态植被模型的输入，以探索漫射辐射对 1981-2015 年全球总初级生产力 (GPP) 的影响。使用更新的K _d，模拟 GPP 在 76 个 FLUXNET 站点中的 72 个站点中显示较低的 RMSE，导致 RMSE 平均降低 9.9%。此外，更新K _{d 的}模拟呈现出比原始K _d更高的全局 GPP (3.1%)来自现代研究和应用回顾性分析 (MERRA) 产品。模拟显示，占总短波辐射的 54% 的漫射辐射对长期全球平均 GPP 贡献了 1.49 g C m ^-2  day ^-1 (64.3%)。1981-2015 年期间，直接辐射的变化导致全球 GPP 趋势为 -0.49 g C m ^-2  yr ^-2，随着漫反射增强，该趋势被 0.31 g C m ^-2  yr ^-2 (53.1%)抵消辐射。