Response of seed germination of the alpine endangered species Rhodiola crenulata to temperature in different years

To study the effects of temperature on seed germination of Rhodiola crenulata, we examined the characteristics of seed germination at eight constant temperatures (1, 5, 10, 15, 20, 25, 30, and 35 ℃) and two alternating temperatures (15 ℃/5 ℃ and 25 ℃/15 ℃) in different years (2014, 2015, 2016, 2019, 2020, and 2021) at Daxueshan Mountain in Shangri-La, Yunnan Province. The results showed that the seeds germinated under a wide temperature range and the germination niche breadth was 0.831～0.891. However, the seeds germinated significantly better at higher temperatures (15～25 ℃), and the alternating temperatures had no significant effects on seed germination. Cardinal temperatures (T_b, T_o, and T_c) were 0.49～0.82 ℃, 19.38～20.88 ℃, and 34.21～38.76 ℃, respectively, and the thermal time for 50% (t₅₀) germination ranged from 40.7 to 67.11 ℃·d. Low base temperature and wide germination niche breadth made the seeds germinate soon after snowmelt at the beginning of the short growing season, which maximizes the duration of the seedling growing season. The R. crenulata seeds exhibited “opportunistic” germination behavior with a wider germination window. The focus of this study was on the effects of temperature on seed germination of R. crenulata, and the findings provided reference materials for the protection and utilization of R. crenulata.