Light-use efficiency (LUE) describes conversion of incident light into gross primary production (GPP), combining the inherent photosynthetic efficiency of chloroplasts with light-capture ability of the autotrophic community. In lotic ecosystems, LUE is poorly constrained, in part because most studies neglect water-column attenuation. We hypothesized that rigorous quantification of benthic light would (1) improve GPP predictions and (2) constrain cross-site variation in LUE. We used a field-validated light model to successively attenuate open-sky irradiance through the riparian canopy and water column to estimate benthic light at 11 sites spanning discharge and dissolved-color gradients where we simultaneously calculated daily GPP. Our results indicate substantial water-column attenuation (up to 96% of stream-surface light), implying significant underestimation of LUE using stream-surface light alone. Benthic light dramatically improved GPP predictions, especially after considering mean-light conditions, which we suggest enumerates ecosystem light-capture ability due to biomass density. The model including mean-light effects explained 78% of GPP variation across sites and yielded a LUE identical to terrestrial ecosystems (1.9%). Interactions between daily and mean-light only slightly improved model fit (R² = 0.80), implying higher LUE at sites with higher mean light, but notably reduced LUE variation across sites compared with individual site analyses. This suggests that better representation of benthic light regimes leads to LUE convergence. Our study supports use of a global river LUE to translate large-scale predictions of stream light regimes into expected GPP, from which disturbance and nutrient limitation effects can then be discerned.

光利用效率（LUE）描述了将叶绿体固有的光合作用效率与自养群落的光捕获能力相结合的方式，将入射光转换为初级生产总值（GPP）。在抽水生态系统中，LUE的约束性很差，部分原因是大多数研究都忽略了水柱衰减。我们假设对底栖光的严格量化将（1）改善GPP预测，（2）约束LUE中的跨站点变化。我们使用了经过现场验证的光模型来连续衰减通过河岸冠层和水柱的开阔天空辐照度，以估计11个分布在排放和溶解颜色梯度上的底栖光，同时我们同时计算了每日GPP。我们的结果表明，水柱的衰减很大（高达溪流表面光的96％），意味着仅使用流表面光会大大低估LUE。底栖光显着改善了GPP预测，尤其是在考虑了平均光条件之后，我们建议枚举由于生物量密度而引起的生态系统光捕获能力。包括平均光效应的模型解释了整个站点GPP差异的78％，并产生了与陆地生态系统相同的LUE（1.9％）。每日光照与平均光照之间的交互仅略微改善了模型拟合（包括平均光效应的模型解释了整个站点GPP差异的78％，并产生了与陆地生态系统相同的LUE（1.9％）。每日光照与平均光照之间的交互仅略微改善了模型拟合（包括平均光效应的模型解释了整个站点GPP差异的78％，并产生了与陆地生态系统相同的LUE（1.9％）。每日光照与平均光照之间的交互仅略微改善了模型拟合（R ²  = 0.80），这意味着平均光较高的位点的LUE较高，但与单个位点分析相比，整个位点的LUE变化明显减少。这表明更好地表示底栖光态会导致LUE收敛。我们的研究支持使用全球河流LUE将流光模式的大规模预测转化为预期的GPP，然后可以从中识别干扰和营养限制效应。