Abstract: Drought is a crucial factor affecting seed germination and seedling growth of desert plants. In the study, we examined the effects of seed size (large, small) and bract (without bracts, with bracts) on seed germination and seedling growth of Ceratoides arborescens, a perennial super xerophyte semi-shrub, under different drought levels (0, 100, 200, 300 and 400 g·L^-1 PEG6000). The results showed that drought stress significantly inhibited seed germination and reduced shoot length of seedlings. Under the 100 and 200 g·L^-1 PEG6000 stress conditions, root length of seedlings were significantly increased, whereas it was significantly reduced under the 300 and 400 g·L^-1 PEG6000 stress intensities. The presence of bract significantly reduced seed germination percentage by 12%, germination index by 50.5%, and shoot length by 20.8%, but increased root length by 6.3%. Seed size did not affect seed germination index. Compared with small seeds, germination percentage of large seeds was 3% higher, shoot length and root length of seedlings were 20.5% and 33.0% higher, respectively. In summary, seed bract in C. arborescens through delaying seed germination and seed size through influencing the survival of the early state of seedling were the most important strategies to adapt extremely arid environment.

Key words: Ceratoides arborescens, drought, seed, bract, germination, seedling