Vapor Pressure Deficit Dominates the Seasonal Dynamics of Water Use Efficiency in Platycladus orientalis Plantations in Beijing Mountainous Areas

GAO Yao, ZHOU Ze-yuan, LI Fei-fei, HU Dong-yang, ZHANG Yong, YU Hai-qun, LI Xin-hao, ZHAO Hong-xian, LI Qin-yuan, LIU Peng, ZHA Tian-shan   

  1. Beijing Forestry University, State Key Laboratory of Efficient Production of Forest Resources 100083, China
    Beijing Forestry University, School of Soil and Water Conservation 100083, China
    Beijing Forestry University, Beijing Engineering Research Center of Soil and Water Conservation 100083, China
    , The Beijing Center for Forest Resource Planning and Monitoring 100193, China
    , Beijing Ming Tombs Forest Farm Management Office 102200, China
    Northwest Agriculture and Forestry University, State Key Laboratory of Soil and Water Conservation and Desertification Control 712100, China
  • Received:2025-09-05 Revised:2025-11-19
  • Contact: ZHA, Tian-shan

Abstract: To optimize stand management, enhance water regulation and carbon sequestration functions, this study explored the response mechanisms of water use efficiency (WUE) to key water-related factors in plantation ecosystems. A typical Platycladus orientalis plantation ecosystem in the mountainous area of Beijing was selected as the study site. Based on eddy covariance observations and the TEA model for evapotranspiration partitioning, ecosystem scale WUE (WUEET) and canopy scale WUE (WUET) were derived to analyze their temporal dynamics and the regulation mechanisms of water-related factors. During the growing season, the mean values of WUEET and WUET were 5.93±2.03 and 7.65±2.42 g C·kg–1 H2O, respectively, with consistent variation patterns. Vapor pressure deficit (VPD) was identified as the dominant factor controlling both WUEET and WUET: across different soil water content (SWC) quantiles, both indices exhibited significant negative sensitivities to VPD, primarily due to enhanced evapotranspiration (ET) and transpiration (T) under higher VPD, while gross ecosystem productivity (GEP) was not significantly suppressed. When SWC<0.20 m3·m−3, the negative sensitivity of WUET to VPD was stronger than that of WUEET. In contrast, under varying VPD conditions, both WUEET and WUET showed weak sensitivities to SWC, likely because GEP, ET, and T responded similarly to SWC changes, weakening its regulatory effect on WUE. With increasing air temperature (Ta) and photosynthetically active radiation (PAR), the negative sensitivity of WUEET and WUET to VPD gradually declined, while their sensitivity to SWC remained low. This study highlights the dominant role of atmospheric drought in regulating WUE across multiple scales in plantation forests, providing a scientific basis for developing precise water-management strategies and enhancing carbon-sink functionality in mountainous plantation ecosystems.

Key words: coniferous forest, sensitivity, carbon-water coupling, water use strategy, Beijing Mountainous Areas

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