Elevated [CO2 ] alleviates the impacts of water deficit on xylem anatomy and hydraulic properties of maize stems.

Plants can modify xylem anatomy and hydraulic properties to adjust to water status. Elevated [CO₂ ] can increase plant water potential via reduced stomatal conductance and water loss. This raises the question of whether elevated [CO₂ ], which thus improves plant water status, will reduce the impacts of soil water deficit on xylem anatomy and hydraulic properties of plants? To analyze the impacts of water and [CO₂ ] on maize stem xylem anatomy and hydraulic properties, we exposed potted maize plants to varying [CO₂ ] levels (400, 700, 900, 1200 ppm) and water levels (full irrigation, deficit irrigation). Results showed that at current [CO₂ ], vessel diameter, vessel roundness, stem cross-section area, specific hydraulic conductivity and vulnerability to embolism decreased under deficit irrigation; yet, these impacts of deficit irrigation were reduced at elevated [CO₂ ]. Across all treatments, midday stem water potential was tightly correlated with xylem traits and displayed similar responses. A distinct trade-off between efficiency and safety in stem xylem water transportation in response to water deficit was observed at current [CO₂ ], but not observed at elevated [CO₂ ]. The results of this study enhance our knowledge of plant hydraulic acclimation under future climate environments and provide insights into trade-offs in xylem structure and function.