1 Background As global warming intensifies atmospheric drying, rising atmospheric vapor pressure deficit (VPD) has rapidly emerged as an important hydroclimatic stressor facing terrestrial ecosystems, not merely by reducing soil-water availability, but by exerting direct atmospheric pressure on plant hydraulics and carbon assimilation (Joshi et al. 2022). This represents an emerging shift from a warming-dominated to a drying-dominated stress regime (Gebrechorkos et al.