DORMANCY AND GERMINATION IN SHORT-LIVED LEPIDIUM PERFOLIATUM L. (BRASSICACEAE) SEEDS

To understand germination timing in an ecological context, the response to environmental events that effect seed dormancy is central and has to be combined with knowledge of germination responses to different ecological factors. In this study, seed dormancy, germination and seedling survival of annual short-lived clasping pepperweed Lepidium perfoliatum L. (Brassicaceae) were investigated. Three types of pre-treatments viz., various temperature dry storage, light and water stress were tested as possible dormancy-and survival-affecting environmental events. Fresh mature seeds were greatly dormant. Warm (30 degrees C) dry storage more facilitated breaking dormancy, they germinated well under apt conditions (e. g. 20 degrees C and 10/20 degrees C plus periodic light, 14 h/d). For those seeds which underwent after-ripening, they could germinate at a range of constant temperatures (4, 10, 15, 20, 25, and 30 degrees C) and one alternating temperature (10/20 degrees C). Under alternating temperature regimes, the final percent germination of L. perfoliatum seeds increased from 37 degrees C to 93% when temperature altered from 4/10 degrees C to 10/20 degrees C in light, then decreased with increasing temperature. The germination pattern under constant temperature conditions was similar to that under alternating temperature and significant differences in final percent germinations and rates of germination were observed among different temperatures. Under different light treatments, final germination of showed significant differences, only with 35% of germination percentage in dark, much lower than those in red and white light (i.e. 93% and 91%, respectively). GA(3) could promote the germination of non-dormant seeds in dark. When water potentials were reduced, final percent germination decreased dramatically, and few seeds germinated at -0.98 MPa (generated by PEG-8000). The changes of proline content in resultant seedlings were reverse to that of final percent germination with changing water potentials. The present findings show that the dormancy and germination patterns of L. perfoliatum are important mechanisms adaptive to the rigorous desert environmental conditions.