Abstract: Several growth and physiological indexes, such as biomass allocation pattern, relative growth rate (RGR), soluble sugar content, membrane leakage rate and semilethal temperature (LT50), of seedlings of three Ligularia species (L. virgaurea, L. sagitta, and L. przewalskii) from the eastern QinghaiTibet Plateau were determined under suitable and simulated low temperature conditions, in order to understand the growth traits, endurance to low temperature, interspecific difference of three seedlings, and their adaptability to alpine environment. The results showed that: (1) Cotyledons of three seedlings extended rapidly at the early stage of seed germination, after which root/shoot ratio increased rapidly, RGR reached the peak after 10-15 days of seed germination, and a significant positive correlation between the root/shoot ratio and biomass accumulation was evident. (2) Survival rates of the three seedlings were more than 70% under 4 ℃, but that of L. przewalskii was relatively lower than those of the other two species. RGR peak was significantly delayed and reduced, and 64% reduction of the RGR peak was caused by decreased root biomass ratio of seedlings. (3) LT50 values of the three seedlings were -8.24, -8.14 and -7.28 ℃, respectively, indicating that the three species could achieve the regeneration of their population via enduring short cold stress at the seedling stage. (4) After low temperature (-5 ℃) treatment, the soluble sugar content increased by 3.61, 2.90 and 1.61 folds and the free proline content increased by 2.57, 4.40 and 37.68 folds in leaves from the three species, respectively, suggesting that the three species can improve their abilities of cold resistance through utilizing different metabolic regulation mechanisms. In conclusion, our results suggest that all the three species of the genus Ligularia have good life history strategies to adapt to the alpine condition in the QinghaiTibet Plateau.

Key words: nitrogen absorption, cucumber, NO₃^--N/NH₄⁺-N ratio, nitrogen metabolism.