Increasing transpiration sensitivity to rising vapour pressure deficit raises US spring wheat yields under current and future climates: a two-model simulation study

Limited wheat transpiration under rising vapour pressure deficit (VPD), i.e. VPD-sensitivity, has been shown to improve yields under terminal drought by conserving water. However, this trait may lead to yield penalties in well-watered environments. Using the US spring wheat belt as a case study, simulations were conducted to assess the effect of genotypic variation in transpiration VPD sensitivity on yield performance across the entire region relative to a genotype not expressing this trait. We used two crop models, APSIM and SSM-Wheat, representing different levels of algorithmic complexity, and historical and future climate scenarios for the 2050s and 2080s based on simulations using 20 global climate models across 457 locations. Regardless of the VPD threshold (1.5 kPa, VPD_1.5 or 2 kPa, VPD_2.0) at which the sensitivity was initiated, this trait led to systematic yield gains (13%–16% for VPD_2.0, 40%–45% for VPD_1.5) under historic climate scenarios across the entire region, regardless of the crop model, with high probability (> 0.8). Large yield benefits (16%–20% for VPD_2.0, 29%–65% for VPD_1.5) are also expected to occur throughout nearly all future climate scenarios, except for the most remote and extreme one (2080s_RCP8.5). Both crop models, however, diverged in identifying regions with the highest levels of yield increase. Overall, this study points to the key importance of introgressing transpiration sensitivity to VPD in US wheat germplasm and to the need for joint analyses of more than one crop model in predicting spatially resolved yield performance due to this trait.