Emilio Quintana Molina

The uncertain effects of climate change pose drought-related challenges in grapevineproducing regions. Novel adaptation measures to climate change through experimental research must be explored for grapevine production in drought-prone areas. Studies indicate that abundant fertilization with potassium aids against harmful drought effects in crops. The objective of the present research was to evaluate the effects of potassium availability on grapevine (Vitis vinifera cv.) physiology and productivity under short but severe drought stress periods through an experimental setup with weighing lysimeters under six treatments based on three potassium levels (concentrations in irrigation water: 5, 15 and 60 mg K+ L -1 ) and two irrigation regimes (well-watered and water-deficit). The study hypothesized that abundant potassium levels enable grapevines' tolerance to drought periods, sustaining plant physiological development and improving yield under episodic drought stress. Whole-tree actual evapotranspiration during the growing season was calculated from water balance in the lysimeters. Midday stomatal conductance (gs) and stem water potential (Ψstem) were measured during two drought trials, and leaf area index (LAI) before, during, and after each trial. Additionally, reference evapotranspiration (ET0) and vapor pressure deficit (VPD) were monitored during trials. The study's results regarding physiological parameters indicate that plant dehydration had similar patterns in gs among treatments in both trials. In contrast, gs recovery was staggered between treatments, with the 60WD treatment the last to recover in both trials. Regarding Ψstem, its behavior during plant dehydration in the first trial was similar among treatments, while in the second trial, differences between treatments were noticeable. Lastly, Ψstem recovered in all treatments on the first day of rehydration in both drought events. Regarding ETa, both drought events suffered a post-drought reduction without reaching similar values as the well-watered treatments. The ETa rate patterns were different between well-watered and water-deficit treatments during severe water stress days. Furthermore, lysimeter coefficients (Klys) were noticeably different regarding crop coefficients (Kc) from the second half of the growing season onwards. In terms of LAI, drought significantly impacted plant canopy development, mainly in consecutive days of severe water stress. Ultimately, short drought events did not affect grapevine yield, water productivity, number of clusters, and brix degrees of the grape juice among treatments. In contrast, it affected average berry and cluster weights mainly between K-5 and K-60 treatments. In sum, the study findings were against the proposed hypothesis.

Gerardo E. van Halsema and Alon Ben-Gal - Supervisors