Physiological, biochemical, and transcriptomic analyses of Panax ginseng leaves to low-temperature stress under different soil water conditions

Low-temperature influences plant growth and the development of quality characteristics. However, water can mitigate certain adverse effects of low-temperature stress by modulating internal plant temperature and supporting essential physiological processes. This study examined physiological responses, transcriptomic changes, and dynamic accumulation of bioactive compounds in ginseng leaves under low-temperature stress across varying soil moisture levels. Results showed that low-temperature inhibited ginseng leaves photosynthetic performance across all soil moisture treatments, particularly in the high soil moisture group (LQ). After 33 h of low-temperature stress, net photosynthetic rate (Pn), stomatal conductance (gs) and transpiration rate (E) decreased by 64.01%, 33.33% and 38.20%, respectively, compared with the 0 h. After 48 h, non-photochemical quenching (NPQ), maximum fluorescence intensity (Fm), and maximum PSII quantum yield (Fv/Fm) declined by 62.76%, 52.93% and 51.29%, respectively, compared with the 0 h. Meanwhile, the LQ group exhibited the most severe lipid peroxidation, with malondialdehyde (MDA) levels increasing by 128.80% after just 4 h of low-temperature stress—indicating compromised membrane integrity and diminished cold tolerance. Notably, under low-temperature stress, all three soil moisture treatments enhanced sucrose synthase (SUSy) and sucrose phosphate synthase (SPS) activity, promoting sucrose accumulation and improving osmotic regulation. Concurrently, they increased total saponin content—primarily PPT-type and PPD-type ginsenosides. Transcriptomic analysis revealed upregulation of key genes in both the starch—sucrose metabolic and ginsenoside biosynthesis pathways. These findings provide a theoretical basis for scientifically formulating ginseng cultivation management strategies by regulating soil moisture conditions under low-temperature stress, which holds significant importance for ensuring ginseng cultivation and industrial development. • Low-temperature stress with varying soil moisture inhibits ginseng PSII activity. • MDA content increased in LQ group leaves, weakening ginseng cold resistance. • Up-regulated genes in starch-sucrose and ginsenoside biosynthesis pathways. • Reasonable water management alleviates cold injury and promotes saponin synthesis.