A Seed Bank Study On The Eastern Alpine Meadow Of Qinghai-Tibet Plateau

The soil seed bank is one of the life history stages of plant populations, which iscalled subpopulation stage, and it is evolutionary memory of plant community whichreflects the evolution of the process of vegetation. Seed bank may function as a typeof genetic memory of a population, and play an important role in communitydynamics and regeneration. Seed bank is the major resource of vegetation restorationafter disturbance, and play a significant role in restoration and reconstruction ofdegraded ecosystem. At present, research of soil seed bank has become a recognizedand indispensable part of plant ecology now and has been an active research area. Sofar, no studies of seed banks from Oinghai-Tibet plateau exist. We through investigatethe size of seed bank, species composition, and relationship of seed bank andaboveground vegetation, attempting to find the distribution pattern of seed bank inthese areas, the role of seed bank in the process of plant communities construction.Moreover, this study provides a theoretical basis for restoration and reconstruction ofdegraded ecosystem in alpine areas.The result showed:1) There rich seed bank resources exist in the alpine meadow of easternQinghai-Tibet plateau. The mean viable seed density was 674 seeds.m^2- 9779seeds.m^-2.2) The density of buried seeds increased significantly with increasing disturbance,but no difference in species richness. Seed density and species richness decreasedwith depth. The proportion of perennial species decreased with decreasing disturbanceboth in seed bank and vegetation. A large portion of species with persistent seeds inthe disturbed areas indicate that it is a strategy of adaptation to current disturbance.3) Detrended Correspondence Analysis (DCA) showed significant differences ofspecies composition between seed bank and vegetation except the seriously disturbedsite. Our results suggest that the establishment of new species in severely disturbedareas is more dependent on the seed bank. The mean seed density was 6105 viableseeds.m^-2 in severely disturbed area, indicating that restoration of disturbed areas isnot seed limited, so the seed bank had a high potential for restoration of species-richvegetation. Oppositely, the restoration in less disturbed and mature meadows does notrely on seed banks, and the establishment of the vegetation in these communities is more likely to rely on seed dispersal and species with vegetative reproduction.4) The seed density in seed banks decreased with successional age, but speciesrichness and diversity increased. Hypotheses about changes in seed bank duringsuccession, predicting decreasing species richness and diversity, were not confirmed.The hypothesis that density of buried seeds declined during succession was confirmed.Similarity between the seed bank and vegetation decreased gradually with successionin the whole. The Vegetation is more similar to the seed bank in the shallow layer thanto the seed bank in the deeper soil, which shows that the vegetation contributes less tothe seed bank as soil depth increases, species of the later successional stagescontributed little to the seed bank. Most of species from early successional stageproduced longer-lived seeds, which stayed viable in the soil for a long period (morethan 20 years). The seed bank was mainly composed of first successional speciesduring the whole successional range.5) The result of NMDS showed that during the course of succession, thevegetation showed a clear successional trend. However, this trend is not reflected inseed bank, and the species composition of seed bank is unvaried during thesuccessional process. We conclude that seed bank play an important role onvegetation in the early succession stage. In the later succession stages, the proportionof perennial was increase, seed bank' role become weaker and weaker, so thecommunity regeneration is likely relies on vegetative reproduction and dispersal.6) The buried seed bank density and species richness decreased with the altitudeincrease whatever in the total or each separate soil layer, transient seed bank orpersistent seed bank. The proportion of perennial species increased with altitudeincrease in aboveground vegetation, but no difference in seed bank. The higheraltitude areas have higher seed bank depletion.7) The persistent seed bank was the most frequent strategy at all three altitudes.There 23.6% species in seed bank changed their strategy in different environment.The hypothesis "the seed bank strategy is a species' inherent trait, i.e.," was notconfirmed in our study.8) Based on the results from three altitudes, we found the seed from persistentseed bank tend to have smaller seeds than species with transient seeds. Seed size wasnegatively correlated with seed frequency, and the tendency increased with altitudeincrease, but the correlation was not significant. This indicated that the smaller seedstend to exist in higher altitude area. The result showed there no relationship between seed size and seed frequency with soil depth increased, so we think there norelationship between seed size distribution and soil depth.9) The result of Sorensen indicated that the similarity of Seed bank andvegetation decreased with altitude increase. The result of NMDS showed that thespecies composition of seed bank and vegetation was low in the whole, and thesimilarity decreased with altitude increase, indicating that the contribution of seedbank to aboveground vegetation community was smaller in higher altitude areas.