Exploring the drought vulnerability of the top spanish grape cultivars

 

Abstract:

Spain is known for hosting the largest vineyard in the world with about 930 kha, being its most iconic cultivars Airén, Bobal, Garnacha Tinta, Garnacha Tintorera, Macabeo, and Tempranillo, which account for almost 65% of the vineyard area. Despite the rootedness of these cultivars, the climate change threatens their future sustainability, so it is of great interest to explore how they will respond to these conditions. Two key physiological traits in plants’ response to drought are the xylem hydraulic conductivity (K_h), which indicates the capacity of stems to transport water, and the point at which plant wilting occurs (or turgor loss point, π_tlp), the moment at which plant survival is at serious risk. This study aims to determine both physiological traits in the top varieties of Spanish wines.

The experiment was performed from July to August 2024 in an experimental vineyard located at IVICAM-IRIAF in Tomelloso (Castilla-La Mancha,  Spain). Airén, Bobal, Garnacha Tinta, Garnacha Tintorera, Macabeo, and Tempranillo were the cultivars included in the study. Measurements in situ of xylem hydraulic conductivity (K_h) were conducted before branches stopped growing by taking under water internodes ~ 40 mm length located in the middle part of the main shoots (1 measurement per shoot), following the hydraulic method. Between 12 and 15 measurements of K_h were collected per cultivar. On the same shoot, xylem pressure (Ψ_x) was measured using a pressure chamber. Then, when the shoots stopped growing, within two weeks the turgor loss point (π_tlp) was measured by osmometry (Bartlett et al., 2012). Five measurements of π_tlp were taken for each cultivar (5 shoots x 1 leaf per shoot). 

K_h measurements were collected over a wide range of Ψ_x (from no-stress to severe stress); this parameter varied within a large range in Bobal cv. (0.86 MPa), while in Airén exhibited a narrow range (0.23 MPa). Despite these differences, the K_h values obtained were very similar in all cultivars, ranging from 27.10 mmol m s^-1 MPa^-1 in Macabeo cv. to 34.63 mmol m s^-1 MPa^-1 in Garnacha Tinta, not allowing to establish significant differences (p > 0.05). As for π_tlp values, on average they ranged from –1.702 to –1.914 MPa, revealing significant differences (p < 0.01) among cultivars. The results suggests that Airén and Macabeo (–1.702 and –1.722 MPa, respectively) could be more vulnerable to turgor loss under drought conditions than other cultivars such as Bobal, Garnacha Tinta or Garnacha Tintorera (from –1.872 to –1.914 MPa). However, further research is needed to support these findings, mainly concerning the xylem hydraulic conductivity.