Dynamics Research Of Soil Seed Bank About Restoration Duccessional Series Of Degraded Grassland In The Songnen Plains Of China

All viable seeds present on or in the soil or associated litter constitute the soil seed bank. The seed bank during the different succession sequences were studied in the Songnen Plains of China on different sampling time. The seedling bank and the seeds production which were related with the seed bank were also investigated. The results showed that: (1) The number of species tended to increase from early to late restoration succession stage, which changed with the sampling time. The seed density decreased from early to late restoration succession stage on April, May, September, and increased on June, July, August. The number of species existed both on aboveground vegetation and in the seed bank were smaller in later stages than in earlier stages, which agrees with precious findings. (2) Shannon-Wiener diversity index increased in succession following series of restoration on April, May, September, and fluctuated irregulately on June, July, August for the differences of input and output of the seeds. (3) There were no differences in the number of species following the different seasons. There were different change patterns in the density of seed banks. The Choris virgata community varied most a lot, then the Leymus chinensis+Choris virgata community. The Leymus chinensis community, Puccinellia tenuiflora+Leymus chinensis community and Puccinellia tenuiflora community varied insignificantly. The Choris virgata seed bank belonged to the typeⅡ of the Thompson and Grime model of soil seed banks of different habitats and the Puccinellia tenuiflora seed bank belonged to the persistent type. (4) The seasonal changes in species diversity were largest at the late succession community. The index of species diversity in Leymus chinensis community decreased, then increased, decreased and increased ultimately. The index of species diversity in Puccinellia tenuiflora+Leymus chinensis community and Puccinellia tenuiflora community decreased firstly, then increased. Choris virgata community and Choris virgata+Leymus chinensis community tended to increase firstly, then decrease. (5) The productions of seeds in 2003 were large in the five communities. But seed bank size of the prior species in the five communities were all smaller than their seeds productions, and 10%,34%,19%,22%,28% respectively of their seeds production. The seeds input were 18.9%, and the output 5.5% of the seed bank in the late succession –Leymus chinensis community. the seeds production were very large in the early community such as the Choris virgata+Leymus chinensis community and Choris virgata community, accounted for 420%and 354%of the total seed bank respectively, while output of seeds were large also ,accounted for 83.8% and 61.5% respectively.