Morphophysiological dormancy synchronizes timing of seed germination of two alpine species of Meconopsis on the Tibetan Plateau to beginning of growing season

Abstract

Timing of seed germination is critical for seedling establishment and growth of the plant to maturity. Theoretically, then, germination of alpine species should be restricted to a period that ensures seedlings will reach a critical size during the short growing season for overwinter survival. We hypothesized that seeds of two alpine monocarpic perennials of Meconopsis germinate only at the beginning of the growing season in early spring and that dormancy synchronizes the timing of germination to this period. We tested the effects of light, temperature, cold stratification and GA3 on germination of Meconopsis integrifolia and M. racemosa in the laboratory and germination responses to temperature during two 2-year periods of seed buried at 4450 m a.s.l. on the Tibetan Plateau. Most fresh seeds of both species were dormant, and the embryo underdeveloped, indicating morphophysiological dormancy (MPD). GA3 promoted embryo growth and germination of seeds. Buried seeds exhibited an annual dormancy cycle. The physiological component of MPD was released gradually in the field during autumn and winter, resulting in embryo growth (release of morphological component of MPD) and germination just after snowmelt in spring. Embryos in seeds that did not germinate the first year remained underdeveloped until the second spring. Delay of seed burial from October until January (simulating a delay in time of seed dispersal) delayed germination for 1 year but did not change the germination season. Thus, our hypothesis that MPD restricts germination to the beginning of the growing season is supported.