Germination Ecophysiology of Seeds of the Winter Annual Chaerophyllum Tainturieri: A New Type of Morphophysiological Dormancy

Abstract

(1) Freshly matured seeds of the native North American winter annual Chaerophyllum tainturieri have morphophysiological dormancy (MPD), which is a combination of morphological (underdeveloped embryos) and physiological dormancy of the non-deep type. (2) Seeds after-ripen at high diurnally fluctuating temperatures (25/15 'C, 30/15 'C and 35/20 ?C) but not at low-constant or fluctuating temperatures (5 'C, 15/6 'C and 20/10 ?C); thus, the breaking of physiological dormancy occurs in the field during summer. Gibberellic acid promotes after-ripening. (3) Light is required for embryo growth, but it is ineffective while seeds are physiologically dormant. Thus, embryo growth and germination occur in autumn, after seeds are no longer physiologically dormant. However, if seeds are exposed to light for two or more days in summer, after the breakage of dormancy has started, they will germinate in darkness at normal autumn temperatures. (4) October habitat temperatures (c. 20/10 ?C) induce dormancy, and consequently no germination occurs in spring. Thus, the species behaves as a strict winter annual, germinating only in autumn. (5) Buried seeds exhibit an annual dormancy-non-dormancy cycle. Seeds become nondormant during summer and re-enter dormancy in autumn. This is the first species in which it clearly has been demonstrated that seeds with MPD can go into and out of dormancy annually. (6) Embryos did not grow while seeds were buried for thirty-two months. A light requirement for embryo growth ensures that buried seeds do not germinate in autumn while they are non-dormant. This is one reason why seeds can form persistent seed banks. (7) Seeds have a type of MPD that has not been described before, and we suggest that it be called 'non-deep simple MPD.' This is the eighth type of MPD so far described for seeds.