Root Hydraulic and Metabolomic Recovery Outpaces Stomatal Reopening in Rewatered Quinoa

Drought research on quinoa has focused almost exclusively on the shoots, leaving the roots, the organ that first senses soil drying, largely unexamined, and its recovery dynamics are still poorly characterized. Here, we show that in the Chilean coastal quinoa ecotype AZ1, recovery from drought is governed belowground, and the root regains hydraulic and metabolomic competence well before the stomata reopen. After 72 h of soil drying, stomatal conductance (g_s) decreased by 98%, whole-plant transpiration declined biphasically (~92% of the loss within the first two hours), and water potential decreased steeply at the soil-root interface (with soil and root water potential declining approximately 10- and 20-fold relative to well-watered plants), while the stem remained near-stable, pinpointing the root as the dominant hydraulic bottleneck. Twenty-four hours after rewatering, root system and whole-plant water potential, osmotic root hydraulic conductance (Lp_rOS), root anatomy, and the polar metabolome were largely restored, yet g_s remained statistically indistinguishable from droughted plants. Strikingly, hydraulic recovery proceeded without rebuilding the osmotic sugar pool; instead, normalization of TCA-cycle intermediates points to an energy-powered and possible aquaporin-mediated transport route that bypasses still-suberized apoplastic barriers. Root system metabolomics, led by GABA and L-alanine, which overshot the control, tracked root rehydration but correlated negatively with g_s, suggesting that nitrogen-rich solutes may act as candidate belowground cues restraining stomatal reopening. These findings suggest that the quinoa root system acts as a pacemaker for drought recovery.