Accurately quantifying ecosystem respiration (ER) is crucial for understanding the feedback between the terrestrial carbon (C) cycle and climate change. However, the current estimation of ER by partitioning net ecosystem exchange (NEE) meets a great challenge due to the response difference of daytime and nighttime respiration to temperature and the effects of air humidity. In this study, we modified daytime flux partitioning methods to estimate ER by integrating the different daytime and nighttime temperature sensitivities of ER (E_{0, day} and E_{0, night}, referred to as DT-E₀) and then relative humidity (DT-RH) based on eddy covariance and isotopic data at three sites. Our results showed that diurnal and seasonal patterns of daytime ER derived from DT-E₀ and DT-RH agreed well with isotopic data, but were considerably different from previous widely used methods (e.g., nighttime (NT) and daytime (DT) methods). The daily mean ER with DT-E₀ was 6%∼18% less than those with NT and DT, suggesting that the difference between E_{0, night} and E_{0, day} greatly affects ER estimates. By adding RH, the difference in mean ER estimated by DT-RH and DT-E₀ was largest in the dry period at CN-Qia, suggesting that the change in RH at dawn and dusk may significantly influence ER and E₀ in the water-limited season. In addition, the magnitude of inhibition by light in the daytime ER from DT was less than that from DT-RH, especially in forest ecosystems, indicating the previous underestimation of light inhibition for ER. Our study highlights the crucial importance of diurnal variations in E₀ and RH in accurately estimating ER, which may need to be incorporated into regional and global models to improve the assessment of global C budgets.

准确量化生态系统呼吸 (ER) 对于了解陆地碳 (C) 循环与气候变化之间的反馈至关重要。然而，由于昼夜呼吸对温度的响应差异和空气湿度的影响，目前通过划分净生态系统交换（NEE）来估计 ER 遇到了很大的挑战。在本研究中，我们修改了白天通量划分方法，通过整合 ER 的不同白天和夜间温度敏感性（E _0，白天和 E _0，夜晚，简称 DT-E ₀）和相对湿度（DT- RH）基于三个站点的涡流协方差和同位素数据。我们的结果表明，来自 DT-E 的日间 ER 的昼夜和季节模式₀和 DT-RH 与同位素数据非常吻合，但与以前广泛使用的方法（例如，夜间 (NT) 和白天 (DT) 方法）有很大不同。DT-E ₀的日平均 ER比 NT 和 DT 低 6%~18%，表明 E _0，夜间和 E _0，白天之间的差异极大地影响了 ER 估计。通过加入RH，DT-RH和DT-E ₀估计的平均ER差异在CN-Qia干旱期最大，表明黎明和黄昏RH的变化可能显着影响ER和E ₀在限水季节。此外，DT 白天 ER 的光抑制程度小于 DT-RH，尤其是在森林生态系统中，表明先前对 ER 的光抑制的低估。我们的研究强调了 E ₀和 RH的日变化在准确估计 ER 中的关键重要性，可能需要将其纳入区域和全球模型以改进对全球 C 预算的评估。