| The water-lever-fluctuating zone is an important component of the ecosystem in reservoir area, and the vegetation play an important role on the purification of pollutants, the protection of water quality, soil and water conservation, etc. The seed invaded and settled down at the water-lever-fluctuating zone is the precondition and foundation of seed germination, vegetation establish. The construction of the dam destroyed the change of natural fluvial hydrology and hydrodynamic model, changed the important ecological process. It influenced the seed spreading and settling process, which lead to the damage of original plant community in the water-lever-fluctuating zone, and the vegetation could hardly be restored.In this paper, we studied the distribution pattern of soil seed bank in the water-lever-fluctuating zone of Danjiangkou reservoir; revealing the influence mechanism of the flow process under artificial regulation to the seed spreading there. That’s has an significant meaning to the vegetation conservation, and provides theoretical basis for the vegetation restoration in the water-lever-fluctuating zone.The paper studied the distribution pattern of soil seed bank from three different gradient levels. The first gradient level was based on the effect of lateral flow, the study area was divided into " upper zone "(149-156m)," middle zone "(144-149m)," lower zone "(139-144m) three zone according to the interference intensity of water level regulating from weak to strong. The second gradient level was based on the effect of longitudinal flow; the study area was divided into " upstream "," Han reservoir ",’connected area "," Dan reservoir "," front of the dam " and " downstream " six areas according to the interference levels of river flow. The third gradient level was based on the double effects of lateral and longitudinal flow, the soil was divided into "0-5cm layer" and "5-10cm layer ". Refer to the characteristics of water level variation, made the study on the time pattern of soil seed bank in two different months. To studied the soil seed bank by seed germinating experiment and the soil properties. Made the CCA analysis to the soil physical, chemical properties and soil seed bank, the conclusions were as follows:(1) According to study the lateral flow effects on the spatial distribution of the seed bank under different gradient regulating disturbance in water-level-fluctuating zone, the results showed that the difference of soil seed bank density in different zones were significant, and the soil seed bank density increased along with the water disturbance gradient level rising; the " middle zone " was maximum in4index of soil seed bank diversity. It indicated that the lateral flow has a significant influence on the process of seed redistribution in the water-level-fluctuating zone. CCA analysis between the soil seed bank and soil physicochemical properties of different zones in the water-level-fluctuating zone, it showed that, the main influencing factors to the seed bank species distribution in " upper zone " and " middle zone " are the same, both were the pH and the sand content in soil mechanical composition, while in the " lower zone ", the powerful influencing factors to the species distribution of seed bank were the soil bulk density and clay content in soil mechanical composition.(2) The longitudinal flow effects on the density and diversity characteristics of the seed bank. The results showed that the difference of soil seed bank density among different regions was significant, in0-5cm of the soil, the " upstream " and " front of the dam " had lower seed bank density than the " downstream "; while in5-10cm of the soil, only the " upstream " had a lower seed bank density than the " downstream ". In0-5cm of the soil, the diversity of soil seed bank species was minimum in the " front of the dam ", and it was highest in the " connected region "; in5-10cm of the soil, the minimum diversity of soil seed bank in species were the " upstream ",and the highest one was the " downstream ". It indicated that the construction of the dam has a significant influence on the distribution of soil seed bank. According to CCA analysis between the soil seed bank and soil physicochemical properties in different regions of the water-level-fluctuating zone, the results showed as follows:the maximum influencing factors to the seed bank species distribution in the " upstream " were the soil bulk density and clay content in soil mechanical composition; the " Han reservoir " were the pH and the silt content in soil mechanical composition; the " connected region " were the pH and the sand content in soil mechanical composition; the " Dan reservoir " were the soil organic matter and the clay content in soil mechanical composition; the " front of the dam " was the pH; the " downstream " were the pH value and the clay content in soil mechanical composition. The powerful influencing factors were not exactly the same to the distribution of seed bank in different regions of the water-level-fluctuating zone.(3) Studied on the density and diversity of soil seed bank in vertical distribution, the results showed that the density of soil seed bank was higher in the "0-5cm layer " than that in the "5-10cm layer " of all zones, and it was all the same in the study areas except the " front of the dam ". It indicated that the water flow increased the reserves of soil seed bank, and the reserves of soil seed bank might be closely related with the ability of seeds to spread. According to CCA analysis between the soil seed bank and soil physicochemical properties in different soil depth of the water-level-fluctuating zone, the results showed that the maximum influencing factors to the seed bank species distribution in "0-5cm layer "were the content of soil organic matter and the silt content in soil mechanical composition, while in "5-10cm layer " were the pH value and the clay content in soil mechanical composition. The powerful influencing factors to species distribution were exactly different in0-5cm and5-10cm soil layer, and the species distribution of the seed bank in deep soil layer were all gathered at the center of the seqencing axes.(4) The density of the soil seed bank showed a descend trend with the passage of time. Aspect of species, some species appeared only in April, did not appear in June, and there was no species appeared in June only. The diversity of the species in soil seed bank showed a descend trend with the passage of time, but the difference was not significant, indicating that the dynamic change of time is not the major factors affected the species diversity of soil seed bank.(5) There are39species, belonging to34generas of20families; it was in the medium level aspect of the species richness in the soil seed bank of the water-level-fluctuating zone. There are annuals23, the quantity of these seeds take up90.52%of the total in soil seed bank; there are herbs16, the quantity of these seeds take up9.48%of the total in soil seed bank; There were neither shrubs nor trees seeds appeared. In terms of life form, the annuals are preponderance apparently. |
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