Grapevine rootstocks display trade-offs between desirable water-use traits under elevated temperature

Grapevine rootstocks have been extensively characterized for their agronomic performance and drought tolerance. However, how these traits affect their adaptation to climate change remains a hypothesis. The goal of this study was to assess how an increase of 4°C can influence the behaviour of grapevines grafted onto rootstocks with a wide range of vigour/drought tolerance. For this purpose, three-year-old 'Grenache' plants grafted onto 420A, Fercal, 110R and 140Ru were grown in temperature gradient greenhouses (TGGs) at ambient (T_amb) or elevated (T_+4°C) temperature. After harvesting the fruit, irrigation was withheld down to full stomatal closure point (gs < 0.01 mol H₂O m^-2 s^-1) to characterize the water relations of these plants. Elevated temperature increased stomatal conductance and decreased leaf abscisic (ABA) levels. However, significant interactions suggested a lower sensitivity of 140Ru to elevated temperature. Evapotranspiration (ET) measured with pot lysimeters confirmed that 140Ru consumed more water than 420A. The daily patterns of ET showed that the maximal transpiration rate was shifted towards the earlier hours of the day on hotter days. This early stomatal opening and closure was key to buffer daily ET increases as temperature rose. The drought susceptibility of 420A was characterised by a lower hydraulic conductivity, lower ¹³C discrimination (δ¹³C), higher ABA levels under well-watered conditions, and stomatal closure that manifested at higher stem water potentials and pot matric potential, alongside lower leaf ABA levels. This suggests that water uptake ceases at higher tension in 420A inducing stomatal closure. In conclusion, 140Ru displayed drought tolerance and a low sensitivity to elevated temperature, however, this trait comes at the cost of being the rootstock with the highest water use tested.