Warming offsets productivity losses from high evaporative demand in a widespread pasture grass

· Atmospheric warming and high vapour pressure deficit (VPD) often co-occur, reducing plant productivity by constraining stomatal, biochemical, and respiratory processes. However, their independent effects remain poorly resolved, limiting predictive accuracy.· We experimentally isolated the effects of warming and VPD on the growth and physiology of the perennial C3 pasture grass Dactylis glomerata using controlled-environment chambers with factorial combinations of temperature (26 °C and 30 °C) and VPD (low, 1 kPa; high, 2.4 kPa).· Warming and VPD interacted to constrain plant productivity, primarily through increased respiratory demand and greater predawn stomatal conductance without a corresponding increase in carbon gain, with high VPD imposing a stronger limitation at ambient than elevated temperature. High VPD reduced photosynthetic capacity by decreasing Rubisco carboxylation at ambient temperature and limiting RuBP regeneration across temperature treatments, likely due to chronic reductions in stomatal conductance. Both photosynthesis and respiration acclimated to warming; however, these responses were moderated by atmospheric dryness.· These findings highlight the critical role of VPD, independently and in combination with temperature, in regulating productivity via coordinated effects on carbon metabolism and plant water relations; accounting for VPD effects is therefore essential for forecasting plant responses to future warmer, drier climates.