Seed germination characteristics of annual species in temperate semi-arid region

Annual species is an important part of vegetation of Horqin sandy land, which locates in temperate semi-arid zone of northern China. Seed germination behavior plays a key role in the persistence and dynamics of annual desert plants, but germination data in this region is not available. Accordingly, using a standardized procedure, a laboratory experiment was made on the seed germination for 23 annual species collected from a wide range of habitats in the western regions of Horqin sandy land. Measurements were conducted on freshly collected seeds and on samples subjected to chilling in natural filed soil and dry storage in laboratory for about 150 days. The germination characteristics observed in this study leads us to the conclusion that certain regenerative mechanisms of some species in the field and is favor of conservation, restoration and management of plant communities or species.Significant differences were observed in the capacity of freshly collected seeds for immediate germination. Five species attained germination values above or near 90%, but 11 species failed to exceed 70%, which indicated that these freshly collected seeds have more or less dormancy mechanism. After chilling and dry storage for 150 days, two of five species with high germination values of freshly collected seeds, still maintained high germination values greater than 90%, and other three species decreased, which seems to be the secondary dormancy after storage. Most species that germination percentage of freshly collected seeds was under 80%, germination percentage increased to exceed 80%, some even attain 100%, which showed that freshly collected seeds of most annual species have post-maturation mechanism and they can germinate under favorable environmental conditions in the beginning of a growth season. For three species (A. scoparia, C. glaucum, E. pilosa), their seed germination values were under 70% in different treatments, which means that seeds of these species had stronger innate dormancy; Chilling and dry storage to break dormancy were not significant for seeds of E. pilosa and A. scoparia (P0.05), but chilling was more significant than dry storage to break seed dormancy for C. glaucum; the trait that the fraction of viable seeds did not germinate even in favorable conditions is a benefit strategy to avoid risks in severe desert. Under the experimental conditions, germination time required for 50% and 90% of the final germination percentage to be attained is very short, which indicates that most of the annual species showed the potential for rapid germination, but Artemisia scoparia, Chenopodium Glaucum, Kochia sieversiana and Agriophyllum squarrosun had longer germination duration in different treatments, which may be another favorable strategy. The relationships of germination mechanisms and adaptability to uncertain desert environments of some mainly annual species were discussed.