Non‐deep simple morphophysiological dormancy in seeds of the rare alpine/subalpline annual <i>Circaeaster agrestis</i> (Circaeasteraceae)

Little is known about seed dormancy and germination of Circaeasteraceae, an early-diverging eudicot family. This study investigated the seed dormancy-breaking and germination requirements of Circaeaster agrestis, an annual herb in subalpine and alpine regions of the Himalaya-Hengduan Mountains and neighbouring ranges in China. Temperature requirements for embryo growth and dormancy-break were investigated using a move-along experiment. We examined effects of dry after-ripening (DAR) and GA₃ on dormancy release, and ability to form a soil seed bank in the field. Germination responses to various light and water potentials at 5/1°C, 15/5°C, and 25/15°C were determined after 6 months of DAR. At seed dispersal in autumn, the embryo length:seed length (E:S) ratio was 0.29, increasing to 0.61 just before germination. Fresh seeds failed to germinate within 4 weeks under any temperature regime in light or dark. Thus, seeds possess morphophysiological dormancy (MPD). After 16 weeks of incubation at 1°C, embryo growth and germination occurred at 5/1°C or higher temperatures, confirming simple MPD. Based on fresh seed responses to GA₃, DAR and the move-along experiment, buried photoblastic seeds may form a small persistent seed bank. Low winter temperatures alleviate the PD component of MPD, enabling rapid embryo growth and germination with increased temperatures in early spring. However, embryo growth and germination are also influenced by soil moisture and light in spring. We conclude that C. agrestis seeds have nondeep simple MPD. This ensures that seed germination occurs at the optimal time-immediately after snowmelt-thereby maximizing length of the growing period and enhancing probability of seedling survival and reproductive success.