Differential responses of microstructure, antioxidant defense, and plant hormone signaling regulation in potato (Solanum tuberosum L.) under drought, alkaline salt, and combined stresses

• Drought and alkaline salt stress disrupted potato growth and leaf microstructure, with the combined stress changes being the most significant. • Drought and alkaline salt stress increased the accumulation of ROS (H 2 O 2 and O 2 - ), osmoregulatory substances (MDA, Pro, SS, AA, GSH, and AsA), and enhanced antioxidant enzyme (SOD, POD, CAT, TPX, APX, GR, GPX, and DHAR) activities. • Drought and alkaline salt stress negatively affected photosynthesis parameters. P n , G s , and T r were significantly reduced, and C i significantly increased after the stress. • Drought and alkaline salt stress increased the contents of ABA, SA, and BRs and decreased the contents of GA 3 and IAA, inducing changes in the expression patterns of hormone-related genes and activating their signaling. • Drought and alkaline salt stress reduced potato tuber yield and quality. The combined stress reduced yield by 54.13 % (2022) and 60.14 % (2023). In the arid and semi-arid zones of Northwest China, soil drought and alkaline salt stress often occur simultaneously and affect plant growth at multiple levels. Potato ( Solanum tuberosum L.) is a food crop sensitive to drought and alkaline salt stresses and is susceptible to yield loss due to environmental impacts. In recent years, most of the research on abiotic stress response in potato has focused on drought and saline single stresses, and the mechanism of potato response to combined drought-alkaline salt stress and its interactions are still unclear. Therefore, a pot experiment was designed in this study and the potato variety ' Atlantic ' was selected as the test material. The effects of drought (25 % PEG-6000), alkaline salt (200 mmol·L -1 NaHCO 3 ) and combined drought-alkaline salt (25 % PEG-6000 + 200 mmol·L -1 NaHCO 3 ) stresses on growth traits, micro- and ultrastructure, reactive oxygen species, osmoregulatory substances, and antioxidant defenses of potato were investigated using no stress (CK) as a control, leaf photosynthesis and endogenous plant hormones, and also analyzed the changes in the expression patterns of genes related to plant hormone signal transduction under different stresses. The results showed that drought, alkaline salt, and combined stress affected growth, leaf anatomy, and photosynthesis, and increased the accumulation of osmoregulatory substances in potato. The scavenging activities of antioxidant compounds and antioxidant enzymes were enhanced in potato, and combined stress treatments significantly damaged potato more than single stresses. In 2022, combined stress caused a marked increase in H 2 O 2 (208.7 %) and O 2 - (455.6 %) content, while in 2023, they increased by 87.5 % and 215.7 %, respectively. SOD, POD, CAT, TPX, APX, GR, GPX and DHAR enzyme activities were increased by 209.13 %, 55.19 %, 152.59 %, 47.13 %, 104.02 %, 347.37 %, 68.45 % and 130.69 % in 2022 compared to CK in the combined stress treatment. In 2023, they increased by 229.81 %, 49.95 %, 160.62 %, 102.16 %, 94.06 %, 505.15 %, 47.00 %, and 121.19 %, respectively. After the stress treatments, the contents of gibberellic acid (GA 3 ) and auxins (IAA) were significantly lower than those in CK, whereas the contents of abscisic acid (ABA), salicylic acid (SA), and brassinosteroids (BRs) increased. Expression of IAA-related genes (AUX1, Aux/IAA, GH3, and SAUR) was up-regulated after stress. ABA-related genes (PYR/PYL, SnRK2, and ABF) were up-regulated after stress, whereas protein phosphatase 2C (PP2C) genes were down-regulated in expression after stress. The GA 3 receptor GID1 and the F-box protein GID2 were up-regulated after stress. Xyloglucosyl transferase TCH4 gene was up-regulated by stress and positively correlated with changes in BRs content. The TGA transcription factor, PR-1 gene, was induced to up-regulate its expression by stress and positively correlated with changes in SA content. Drought, alkaline salt, and combined stress reduced potato tuber yield and quality, which were 54.13 % and 60.14 % lower than CK in combined stress treatments in 2022 and 2023, respectively, which were significantly correlated with changes in physiological and biochemical characteristics and hormone contents of potato plants.