Diffuse radiation is widely known for its higher light use efficiency in ecosystem carbon uptake than direct radiation, which inevitably alters ecosystem evapotranspiration (ET), as plant carbon uptake and water use are closely coupled through leaf stomata. However, although the impact of diffuse radiation on ecosystem carbon uptake has been extensively explored, its impact on ecosystem ET remains unclear on the global scale and across different plant functional types (PFTs). In this study, we explored the impacts of diffuse radiation on ecosystem ET and its coupling to net ecosystem exchange (NEE) based on long-term eddy-covariance observations and the derived diffuse radiation fraction (K_d) at 201 FLUXNET stations. We found that the increase in diffuse radiation results in a net enhancement of ET when K_d was below 0.42-0.48 for most PFTs. Diffuse radiation was more effective in promoting ET than direct radiation because the diffuse fertilization effect (DFE) on NEE tightly regulates ET through stomatal coupling. On average, the efficiency of diffuse radiation (K_d > 0.8) was 1.51 (±0.80) times higher than that of direct radiation (K_d < 0.2) in promoting ET when the PAR level was less than 300 W m⁻², which was lower than the ratio of 2.40 (±0.93) for NEE under the same conditions, because the simultaneous reductions in vapor pressure deficit (VPD) in part offset the enhancement of ET. Consequently, the increase in ET results in a higher evaporative fraction under shaded conditions with more diffuse radiation. We emphasized the importance of considering the DFE on ecosystem ET in assessing aerosol-induced perturbations in the water cycle under the current and future climate.

漫射辐射因其在生态系统碳吸收中的光利用效率高于直接辐射而广为人知，这不可避免地改变了生态系统蒸散（ET），因为植物碳吸收和水分利用通过叶气孔紧密耦合。然而，尽管漫射辐射对生态系统碳吸收的影响已被广泛研究，但其对生态系统 ET 的影响在全球范围内和不同植物功能类型 (PFT) 上仍不清楚。在本研究中，我们基于201 个 FLUXNET 台站的长期涡度协方差观测和导出的漫射辐射分数 (K _{d )，探讨了漫射辐射对生态系统 ET 的影响及其与净生态系统交换 (NEE) 的耦合。}我们发现，当 K 时，漫射辐射的增加导致 ET 的净增强_{大多数 PFT 的d}低于 0.42-0.48。扩散辐射在促进 ET 方面比直接辐射更有效，因为 NEE 上的扩散受精效应 (DFE) 通过气孔耦合紧密调节 ET。平均而言，当PAR水平小于300 W m ^{-2时，扩散辐射（K} _{d > 0.8）的促进ET的效率是直接辐射（K d} < 0.2）的1.51（±0.80）倍。，这低于相同条件下 NEE 的比率 2.40 (±0.93)，因为蒸汽压不足 (VPD) 的同时降低部分抵消了 ET 的增强。因此，ET 的增加导致在具有更多漫射辐射的阴影条件下更高的蒸发分数。我们强调了在评估当前和未来气候下气溶胶引起的水循环扰动时考虑生态系统 ET 的 DFE 的重要性。