The response of vegetation water use efficiency (WUE) to soil or atmospheric moisture conditions has been widely identified in the past decades, however, the relationships between soil-atmospheric coupling and global vegetation WUE remain unclear under different CO emission scenarios at the end of the 21st century. In this study, we investigated the evolution and characteristics of global soil-atmospheric coupling by the atmospheric vapor pressure deficit (VPD) and soil moisture (SM), and vegetation WUE for both the baseline period (1982–2014) and future periods (2015–2100) under four representative pathways using Coupled Model Intercomparison Project Phase 6 data, and then quantified the impacts of soil-atmospheric coupling on global WUE. Results indicate that the global average vegetation WUE will increase significantly in the future, and the SSP5-8.5 is observed at the fastest growth rate at 0.0902 gC kg HO/decade. Global soil and atmospheric are projected to become drier, especially in the Amazon and Patagonia plateaus, the Middle and Lower Yangtze River Plains; however, VPD remains relatively stable after 2050 under the SSP1-2.6 scenario, highlighting the effectiveness of active restoration policies on atmospheric drought elimination. It is revealed that over 82.13% of vegetated land exhibits a negative correlation between SM and VPD, suggesting vegetation is more susceptible to coupled soil-atmosphere, and SM-VPD coupling tend to occur during the warm season. Approximately 47–59% of global vegetated land is dominated by SM-VPD under four climate scenarios, mainly in the 20°–60°N and 20°–40°S. The affected area expands under moderate and high emission scenarios, particularly in croplands and grasslands. As climate warms, low-altitude regions will become more susceptible to VPD, and some temperature vegetation may transfer from reliance on SM-VPD to dependence on SM. These findings enrich the understanding of global vegetation WUE trends and provide deeper insights into soil-atmosphere coupling and WUE interactions.

中文翻译：

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21世纪全球水分利用效率预测及其对水汽压亏缺和土壤水分耦合的响应

过去几十年来，植被水分利用效率（WUE）对土壤或大气湿度条件的响应已被广泛识别，然而，在不同的CO排放情景下，土壤-大气耦合与全球植被WUE之间的关系仍不清楚。 21世纪。在本研究中，我们研究了基线期（1982-2014年）和未来时期（2015年）大气水汽压差（VPD）和土壤湿度（SM）以及植被WUE的全球土壤-大气耦合的演变和特征。 –2100）根据耦合模型比对项目第六阶段数据的四个代表性路径，然后量化土壤-大气耦合对全球WUE的影响。结果表明，未来全球平均植被WUE将显着增加，SSP5-8.5观测到最快增长率为0.0902 gC kg H2O/十年。全球土壤和大气预计将变得更加干燥，特别是在亚马逊和巴塔哥尼亚高原以及长江中下游平原；然而，在SSP1-2.6情景下，2050年后VPD保持相对稳定，凸显了积极恢复政策对消除大气干旱的有效性。结果表明，超过82.13%的植被土地表现出SM和VPD之间的负相关关系，这表明植被更容易受到土壤-大气耦合的影响，并且SM-VPD耦合往往发生在暖季。在四种气候情景下，主要是在北纬 20°–60°和南纬 20°–40°，全球约 47–59% 的植被以 SM-VPD 为主。在中度和高排放情景下，受影响区域会扩大，特别是农田和草地。随着气候变暖，低海拔地区将更容易受到VPD的影响，一些温度植被可能从依赖SM-VPD转变为依赖SM。这些发现丰富了对全球植被 WUE 趋势的理解，并为土壤-大气耦合和 WUE 相互作用提供了更深入的见解。