Studies On Seed Dormancy And Germination Ecology Of Elaeagnus Mollis,a Endemic Plant In China

Elaeagnus mollis is an endangered species that narrowly distributed in south-eastern Loess Plateau of China.Natural regeneration of the endangered populations may be restricted by low seed germination.In this study,seeds of E.mollis were cultured in laboratory and observed in the field in order to explore:（1）the morphology and germination characteristics of seeds at different developmental stages;（2）seed dormancy and dormancy-broken methods;（3）changes of fatty acid and viability in the process of accelerated aging seeds.The questions were solved to reveal the mechanism of limiting population regeneration of E.mollis.The results are as follows:1.The fruits of E.mollis only had corolla tube at 15 d after anthesis,seed coat appeared at 30 d after anthesis,and vacuolated embryos appeared 45 d after anthesis.The structure of embryo is obvious and can germinate at 60 d after anthesis;the long and short axis and weight of fruits and seeds,and thickness of the constructure surrounding seeds,increased at first and then decreased during development,and reached the maximum ranging from 45 to 75 d after anthesis,respectively.The water content of fruits decreased during development,and the decreasing speed was slow at first and then fast.The dry weight and fresh weight increased at first and then decreased before 90 d after anthesis.The fresh weight reached the maximum value（1.08 g/grain）at 60 d after anthesis,and the dry weight increased to the maximum value（0.80 g/grain）at 105 d after anthesis.Seed germination was the highest（17.30%）at 90 d after anthesis.The results suggested that,the development process was composed of three stages.At the first stage（15-45 d）,protective constructures surrounding the embro were mainly formed and there was no accumulation of dry matter of the embro;at the second stage（45-75 d）,dry matter of embro was fastly accumulated and constructures of embro was primarily formed resulting in seed germination,and the protective constructures began to dehydrate;at the final stage（75-105 d）,nutrition in cotyledons was fastly accumulated,and the protective constructures surrounding the embro was largely dehydrated and the fruits became hard,which might be restrain seed germination.2.The fruits and seeds of E.mollis were relatively big,and the embryo with weak plantule was surrounded by hard and permeable seed coat and appendix from the lignified calyx tubes,and more than half of the seeds were incomplete;the freshly intact seeds did not germinate;the scarified seed germination decreased with the increase of temperature.And germination was highest at 5/15℃in continuous darkness;dormancy was weakly released by GA₃and cold stratification（5℃）,but significantly released by variable termperatre stratification and field burial,indicating that seeds had deep physiological dormancy;Germination was significantly enhanced by median drought（-0.6 MPa）and Na Cl（0.34 M）,and decay was inhibited beyond-0.4 MPa osmotic potential and 0.225 M Na Cl.Our results suggest that,germination was constrained resulting from the highly unhealthy and deeply dormant seeds of this species.3.The seed aging was accelerated under the conditions of high temperature and humanity,and the seed vitality of E.mollis was completely lost after accelerated aging for12 days,and the curve of the viability with aging time showed a reversed to"S"type;Leinoleic acid,oleic acid and palmitic acid were the main fatty acids in the E.mollis seeds;there were significant positive correlations between saturated or monounsaturated fatty acids and seed viability,and fatty acids with 20C had signicantly affected effecs.The results suggested that seed viability of this species was easily lost,and it was difficult to form persistent seed bank in the original habitats with high temperature and moisture in summer.In conclusion,seed germination was constrained by high incomplete seeds,deep physiological dormancy,hard testa and loss of the orginal habitats,persistent seed bank could not be formed resulting from relatively big fruits and short longevity.And thus,it is difficult for the populations to recruit.Effective methods of population regeneration include that,enhancing germination by harvesting seeds at the optimal period,scarifying testa and improveing storage conditions and transplanting germinated seedlings to natural populations,and population regeneration can also be realized by constructing artificial seed bank in the field.