Excessive irrigation in orchards can lead to wastage of water resources and instability or reduction in fruit yield. Therefore, this study aims to comprehensively explore the relationships among growth indicators, photosynthetic parameters, apple yield, and water productivity (WP) based on structural equation modeling (SEMD), and develop the appropriate irrigation management strategy for sustainable apple production. A two-year apple irrigation management experiment was carried out with 17 deficit drip irrigation (DDI) treatments, including a control treatment (CK, 100 % ETc) and 4 water deficit degree (W15 %, 85 % ETc; W30 %,70 % ETc; W45 %, 55 % ETc; W60 %, 40 % ETc) during four growth stages: bud burst to leafing stage (I), flowering to fruit set stage (II), fruit expansion stage (III), and fruit maturation stage (IV). Results indicated that transpiration rate (Tr) was more sensitive to water deficit than net photosynthesis rate (Pn), leading to greater instantaneous water use efficiency (WUEi). Compared to the CK, the W15 % DDI treatments at different growth stages slightly reduced Pn and significantly decreased Tr, thereby enhancing WUEi by 14.5 %-14.9 %. W15 % DDI treatments during the early growth stage restrained excessive growth while enhancing fruit development. SEMD analysis revealed that LAI had a significant positive effect on ET with a standardized path coefficient of 0.312 (P < 0.05) in 2021 and 0.498 (P < 0.001) in 2022, and fruit volume had a significant positive effect on ET with a standardized path coefficient of 1.03 (P < 0.001) in 2021 and 1.313 (P < 0.001) in 2022. The stomatal conductance (gs) was identified as the key factor influencing apple yield and WP using SEMD. The gs had an extremely significant positive effect on apple yield, with a standardized path coefficient of 0.356 in 2022 (P < 0.001). The indirect negative effect of leaf area index (LAI) on WP was mainly through its positive effect on water consumption (ET) and ET's subsequent negative effect on WP. Severe water deficits (W60 %) at stage III are inadvisable, as they may lead to apple yield losses exceeding 20 %. The I-W15 %, II-W15 %, II-W30 %, and IV-W15 % treatments synergistically improve both apple yield and WP, suggesting that these DDI treatments could be recommended for growers aiming to achieve sustainable apple production.

中文翻译：

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亏缺灌溉通过抑制过度营养生长和改善光合作用性能来提高苹果的产量和水生产力


果园的过度灌溉会导致水资源的浪费和水果产量的不稳定或减少。因此，本研究旨在基于结构方程模型 （SEMD） 全面探讨生长指标、光合参数、苹果产量和水生产力 （WP） 之间的关系，并为可持续苹果生产制定合适的灌溉管理策略。进行了一项为期两年的苹果灌溉管理实验，使用了 17 次赤字滴灌 （DDI） 处理，包括对照处理 （CK， 100 % ETc） 和 4 次缺水度 （W15 %， 85 % ETc;W30 %，70 % ETc;W45 %， 55 % ETc;W60 %， 40 % ETc） 在四个生长阶段：芽爆至出叶期 （I）、开花至坐果期 （II）、果实膨大期 （III） 和果实成熟期 （IV）。结果表明，蒸腾速率 （Tr） 比净光合作用速率 （Pn） 对水分亏缺更敏感，导致更高的瞬时水分利用效率 （WUEi）。与 CK 相比，不同生育期 W15 % DDI 处理略微降低了 Pn，显著降低了 Tr，从而使 WUEi 提高了 14.5 %-14.9 %。W15 % DDI 处理在生长早期抑制了过度生长，同时促进了果实发育。SEMD分析显示，LAI对ET有显著的正向影响，2021年和2022年的标准化路径系数分别为0.312（P < 0.05）和0.498（P < 0.001），果实体积对ET有显著的正向影响，2021年和2022年的标准化路径系数分别为1.03（P < 0.001）和1.313（P < 0.001）。使用 SEMD 确定气孔导度 （gs） 是影响苹果产量和 WP 的关键因素。 gs 对苹果产量具有极显著的正向影响，2022 年标准化路径系数为 0.356 （P < 0.001）。叶面积指数 （LAI） 对 WP 的间接负向影响主要通过其对耗水量 （ET） 的积极影响以及 ET 对 WP 的后续负向影响。在 III 阶段出现严重的水分不足 （W60 %） 是不可取的，因为它们可能导致苹果产量损失超过 20%。I-W15 %、II-W15 %、II-W30 % 和 IV-W15 % 处理协同提高了苹果产量和 WP，这表明这些 DDI 处理可以推荐给旨在实现可持续苹果生产的种植者。