Abstract: We investigated the effects of drought and salt stresses on seed germination and seedling growth of three Rheum species (rhubarb) at different temperatures (10, 20 and 30 ℃) in an artificial climatic chamber. Polyethylene glycol 6000 and NaCl were used to simulate different intensities of drought and salt stresses, respectively, with pure water treatment as the control check (CK). The results showed that total germination percentage and germination potential of the three rhubarb species were higher under each treatment at 20 ℃. The interaction between 30 ℃ and drought or salt stresses inhibited seed germination and made seedlings failed to establish. At 10 ℃, the abscisic acid (ABA) content of both aboveground and belowground parts of R. palmatum tended to increase with increasing salt stress. At 20 ℃, the contents of gibberellin (GA) and auxin (IAA) in both aboveground and belowground parts of R. palmatum tended to decrease with the aggravation of drought and salt stresses. The ratios of aboveground to underground non-structural carbohydrates (NSC) of the three rhubarb species tended to decrease and then increase with the aggravation of drought. At 10 and 20 ℃, the ratios of aboveground to underground GA of R. officinale tended to increase and then decrease with increasing salt stress, the ratios of aboveground to underground IAA tended to decrease and then increase with increasing salt stress, while the NSC content of both aboveground and belowground parts of R. palmatum and R. tanguticum tended to increase and then decrease with drought exacerbation. The germination index of R. officinale under different treatments was lower than that of the other two species and showed greater susceptibility to temperature and drought stresses. 20 ℃ was the appropriate temperature for the germination of the three species. Higher temperature could exacerbate the harmful effects of osmotic stress on seed germination and seedling growth, but the appropriate temperature could play a certain role in alleviating the osmotic stress. The rhubarb maintains cellular osmotic balance by regulating the content of soluble sugars, starch, and their ratios in different parts of the plant, and maintains physiological and metabolic activities by adjusting hormone content and allocation patterns to alleviate adversity hazards.

Key words: Rheum, osmotic stress, temperature stress, endogenous hormone, non-structural carbohydrate, response mode