Green revolution breeding favored water conservation, but weakened water use sensitivity to rising vapor pressure deficit in US spring wheat.

The global rise in vapor pressure deficit (VPD) threatens crop production. Plants mitigate high VPD by regulating their transpiration rate (TR). Yield is related to TR, but whether genetic yield gains reflect shifts in TR-VPD responses remains debated. Over the last century, US spring wheat yields have tripled in the Midwest. We aimed to determine (i) whether these gains relate to changes in water-use patterns under rising VPD and (ii) to identify underlying traits. We examined whole-plant TR responses to rising VPD under nonlimiting soil moisture in 14 wheat cultivars released over 105 years, representing a gradient in yield potential. Yield was quantified in a common trial, and morphological and hydraulic properties shaping TR-VPD responses were characterized under controlled conditions. Yield gains temporarily coincided with shifts in water-use patterns under rising VPD. Breeding has maintained a restricted water loss under high VPD in all cultivars. However, the tripling of yield potential around the Green Revolution coincided with the linearization of the TR-VPD response and a reduction in evaporative surface area in modern cultivars. This suggests a more effective water use rather than a reduced total water loss. Daily water-use regulation was associated with traits controlling water demand and supply. TR was restricted at lower VPD (VPDBP), but less effectively (higher slope after VPDBP, more linear TR-VPD response) in plants with a high water demand at low VPD, relative to their water channeling ability. These findings highlight opportunities to improve yields by fine-tuning hydraulic traits.