Non-deep physiological dormancy in seeds of two endangered medicinal alpine species of Rhodiola from the Hengduan Mountains of southwest China

We investigated seed dormancy and germination characteristics of two endangered medicinal species, Rhodiola crenulata and R. fastigiata, from the high altitude (alpine) Hengduan Mountains in China. Germination of fresh seeds was tested in light and dark at six constant (1, 5, 10, 15, 20 and 25°C) and three alternating (5/1, 15/5 and 25/15°C) temperatures and again, after six months of dry after-ripening (DAR) and cold-wet stratification (CS). Fresh seeds of R. crenulata germinated to ≥ 80% at 10, 15, 25/15 and 15/5°C in light, but germination was significantly lower at 1, 5, 20 and 25°C. Germination of fresh seeds in dark was 0 to 25% across the range of temperatures. DAR and CS for six months increased germination and/or decreased mean germination time in both light and dark. Fresh seeds of R. fastigiata germinated to > 95% in both light and dark, except at 1°C in light and 1, 5, and 5/1°C in dark, where germination was < 50%. DAR and CS for six months increased germination and/or decreased mean germination time. Seeds of the two Rhodiola species have (conditional) non-deep physiological dormancy. Germination responses to temperature and light prevent seeds from germinating in the autumn of dispersal, but allow them to germinate quickly after snow melt the next spring. This study provides a method for obtaining plants from seeds of the two Rhodiola species for medicinal uses, which could reduce the harvesting pressure placed on natural populations.