Early physiological and biochemical modulation in garlic under drought and high temperature

Drought and high temperature are major abiotic stresses that increasingly threaten crop productivity under climate change. Although responses to individual stresses are widely documented, the combined effects of drought and heat often induce distinct physiological and metabolic adjustments that remain insufficiently understood. This study investigated short-term responses of garlic plants (cv. Istarski crveni) grown under water-available and ambient temperature (W+/T-), water-available and high temperature (W+/T+), drought-induced and ambient temperature (W-/T-), and drought-induced and high temperature (W-/T+) conditions in controlled climate chambers. Morphological and physiological traits (leaf color parameters, chlorophyll fluorescence, and dry matter), together with metabolite profile (abscisic acid, gamma-aminobutyric acid, proline, glycine, serine, glucose, fructose, mannitol), were assessed over an 8-day period using ANOVA and PLS-DA analyses. Exposure to drought reduced substrate water content and induced abscisic acid (ABA) accumulation, followed by increased proline levels and changes in leaf dry matter. When occurring with high temperature, accumulation of osmolytes, including glucose, fructose, and serine was observed, while photosystem II efficiency remained stable. Multivariate analysis revealed that temperature dominated treatment differentiation during first three days, whereas water availability became an important factor from day 4 onwards. Serine and fructose emerged as potential early biomarkers of combined drought and temperature stress, while leaf color and fluorescence parameters emerge as candidate non-destructive indicators of plant stress responses, warranting validation under field conditions.