Instantaneous and lasting effects of drought on grapevine water use

Water deficit limits grapevine water uptake. However, the quantitative contribution of drought to vine water requirements is largely uncharacterized. Thus, we set to explore whole-plant water use during short-term drought events and recovery and associate the proportional reduction in transpiration with changes in vine physiological attributes. We hypothesized that short drought events pose long-term restrictions to transpiration through limitations to canopy development and stomatal conductance (g_s). We used large (2 m³) weighing lysimeters to measure how three short (six-seven days) drought events affected seasonal vine transpiration. We additionally measured the interactions between vine leaf area index (LAI), available water (AW), g_s, or stem water potential (SWP) with transpiration (ET) during drought and recovery. Three recurrent drought events reduced seasonal ET by 848 L vine⁻¹ (11% of the seasonal uptake). Nevertheless, only 50% of the transpiration losses were an immediate response to the drought, while the other half occurred after rehydration, apparently due to lower g_s and LAI. The stress coefficient (K_S) correlated with g_s and SWP during drought, though their interactions depended on phenology and varied from previous reports. The effect of drought on plant water uptake extended beyond the immediate water limitation and affected vines for the remaining season. Practically, LAI measurements could project most of the long-term ET limitations. While the variability of Ks response to changes in g_s or SWP may result in a 16% or 20% error, respectively, the generalized models presented remain the most comprehensive and inclusive options available for predicting grapevine water uptake under drought.