Understanding the characteristics of water use efficiency (WUE) and its controlling factors in the agricultural ecosystem can help us better understand the coupled process between water use and carbon assimilation spatially. The characteristics of the leaf- and ecosystem-level water, carbon and WUE variations as well as their drivers in a kiwifruit orchard were systematically analyzed during the growing seasons of 2018–2020. The results showed that leaf transpiration rate (T_r), net photosynthetic rate (P_n) and instantaneous WUE (WUE_i) in exposed leaves were 2.25–2.77, 8.32–9.44 and 2.53–3.77 times higher than those of shaded leaves. T_r and P_n were significantly affected by photosynthetic active radiation (PAR) and stomatal conductance (g_s). Air temperature (T_a), leaf water vapor deficit (VPD_l) and stomatal conductance (g_s) affected WUE_i through leaf water consumption, while PAR affected WUE_i through leaf photosynthetic process. Averaged evapotranspiration (ET), gross primary productivity (GPP) and ecosystem WUE (eWUE) were 551.30 ± 75.92 kg H₂O m^-2, 1475.37.59 ± 201.25 g C m^-2 and 2.68 ± 0.04 g C kg⁻¹ H₂O, respectively. Global total radiation (R_g), T_a and VPD were the dominant climatic factors affecting ET and GPP, while R_g and wind speed (U₂) were significantly correlated with eWUE (p < 0.01). WUE_u, defined as the ratio of P_n·VPD_l^0.5 a_nd T_r, could be considered as an effective indicator quantifying the coupled relationship between T_r and P_n·VPD_l^0.5 at the _leaf scale. The coupled relationship between ET and GPP was strengthened after incorporating the effect of VPD on GPP due to reduced time lags among GPP, ET and VPD at the ecosystem scale. R_g, T_a, U₂ and VPD contributed to greater effects through ET than that of GPP on eWUE, while the differences between them were reduced after incorporating VPD on GPP, which may be the source of the dependence of iWUE (GPP·VPD/ET) and uWUE (GPP·VPD/ET) on environmental conditions. This study enriches the scarce literature on what drives multi-scale water and carbon in a humid orchard and contributes to improving the understanding of the coupled process of water and carbon incorporating the effect of VPD at leaf and ecosystem scales.

了解农业生态系统中水资源利用效率（WUE）的特征及其控制因素，可以帮助我们更好地理解水资源利用与碳同化的空间耦合过程。在 2018-2020 年的生长季节系统地分析了猕猴桃园叶片和生态系统水、碳和 WUE 变化的特征及其驱动因素。结果表明，裸露叶片的蒸腾速率（T _r）、净光合速率（P _n）和瞬时WUE（WUE _i）分别是遮荫叶片的2.25-2.77、8.32-9.44和2.53-3.77倍。T _r和 P _n受光合有效辐射（PAR）和气孔导度（g _s）的显着影响。空气温度（T_一），叶水蒸气赤字（VPD_升）和气孔导度（克_小号）的影响WUE_我通过叶水的消耗，而PAR影响WUE_我通过光合过程。平均蒸散量 (ET)、初级生产力总值 (GPP) 和生态系统 WUE (eWUE) 分别为 551.30 ± 75.92 kg H ₂ O m ^-2、1475.37.59 ± 201.25 g C m ^-2和 2.68 ± 0.04 g C kg ^-1 H ₂ O，分别。全球总辐射 (R _g ), T _a和 VPD 是影响 ET 和 GPP 的主要气候因素，而 R _g和风速（U ₂）与 eWUE 显着相关（p < 0.01）。WUE _ü，定义为P的比率_Ñ ·VPD_升^0.5一_Ñ dŤ _{- [R} ，可以被认为是一种有效的指示器量化T之间的耦合关系_{- [R}和P _ñ ·VPD_升^0.5在_升EAF规模。由于在生态系统尺度上 GPP、ET 和 VPD 之间的时间滞后减少，因此在纳入 VPD 对 GPP 的影响后，ET 和 GPP 之间的耦合关系得到加强。ř_克，T_a , U ₂和VPD通过ET比GPP对eWUE的影响更大，而在GPP上加入VPD后两者之间的差异缩小，这可能是iWUE（GPP·VPD / ET）依赖的来源和uWUE (GPP·VPD/ET) 关于环境条件。这项研究丰富了有关驱动潮湿果园中多尺度水和碳的稀缺文献，并有助于提高对水和碳耦合过程的理解，其中包括 VPD 在叶和生态系统尺度上的影响。