Seed Dormancy And Germination Characteristics Of Three Annual Asteraceae Species

Echinops gmelinii, Epilasia acrolasia and Koelpinia linearis are three annual Asteraceae specieswidely distributed in the cold desert of Central Asia. Seed dormancy and germination characteristics ofthese species were reported in this study. Our main aims are to provide a theoretical basis for revealing theplasticity of seed germination time and its restriction factor, and exploring strategies of adaptation ofannual Asteraceae species to the special environment of cold desert of Central Asia. The main results weredescribed as follows:(1) The natural dispersal unit of E. gmelinii is a capitulum and that of E. acrolasia and K. linearis isan achene. Each capitulum of E.gmelinii produces only one seed enclosed by outer, middle and innerphyllaries, which vary in shape and amount of pubescence at base. Seeds of E. acrolasia are blackish,cylindric and have a well-developed pappus, which is gray, slender and long plumose. Seeds of K. linearisare brownish, columnar-scorpioid and epappose, and its pericarp highly lignified and has abaxial shortneedlelike prickles.(2) A low percentage of freshly seeds of K. linearis and E. acrolasia were nondormant andgerminated to low percentages over the range of temperatures, whereas seeds of E. gmelinii were dormantand did not germinate at any condition. As seeds of the three species afterripened(after1month), theygerminated over the range of temperatures. Thus, seeds of the three species have physiological dormancy(PD). Whether seeds germinated in autumn or spring depends on soil moisture. Mechanical resistance ofthe pericarp and of phyllaries reduced germination of E. acrolasia and E. gmelinii, respectively.(3) The temperature requirements for germination as seeds of the three species come out of dormancydo not correspond to any of the5types of non-deep physiological dormancy (PD) previously described.Thus, a sixth type is recognized in which germination occurs over the same range of temperatures in theearly and late stages of dormancy break. Type6would allow seeds to germinate at high or lowtemperatures, whenever soil moisture was nonlimiting. This new type of nondeep PD may be an adaptivestrategy of three annual Asteraceae species in the unpredictable environment of cold desert of Central Asia.