Cortical Integrity Sustains Radial Hydraulic Conductivity Under Acute Salinity in Grapevine Roots

Salinity disrupts plant water transport by altering fine root structures and constraining radial water movement. However, the extent to which hydraulic decline reflects osmotic effects versus structural disruption remains unclear in woody crops, such as grapevines. Here, we combined root pressure probe measurements, exudation assays, and fluorescence microscopy with gravimetric estimates of nighttime water flux to examine how fine-root structural and hydraulic traits co-vary under salinity conditions. Two hyper-arid-adapted grapevine genotypes from Chile's Atacama Desert (R-65 and R-70, Vitis vinifera) and two commercial rootstocks (101-14Mgt and 110-R) were exposed to increasing NaCl concentrations (0, 75, 120, and 250 mM). Under severe salinity, commercial rootstocks exhibited higher root osmolality but stronger declines in radial hydraulic conductivity and greater cortical disruption. In contrast, R-65 and especially R-70 maintained higher hydraulic conductivity together with better preservation of cortical integrity and increased barrier-associated fluorescence. These patterns indicate that hydraulic performance is more closely associated with structural preservation than with the magnitude of osmotic accumulation. Sustained nighttime water flux, particularly in R-70, co-occurred with this preserved hydraulic state but did not provide evidence of a causal coupling. Overall, the results identify coordinated variation among root structure, hydraulic function, and whole-plant water flux under acute salinity, and highlight cortical integrity as a key feature associated with short-term hydraulic responses in grapevine roots.