Soil Seed Bank And Habitat Properties Of Water-Level-Fluctition Zone In Danjiangkou Reservoir Area

The periodical fluctuation of water-level in Danjiangkou Reservoir causes the variation of the wet and dry state of the water-level-fluctuation zone, which would inevitably lead to the difference of soil physical and chemical properties and soil seed bank species. In this paper, we studied soil physical and chemical properties and soil seed bank changes in this special environment to explore the response of soil seed to the water level changes. It can provide theoretical basis for vegetation restoration and reconstruction of water-level-fluctuating zone in Danjiangkou Reservoir Area.According to the practical situation of the water-level-fluctuation zone, We divided the upstream zone to4districts. There are the Dan Reservoir district, the district between Dan and Han Reservoir, the northern Han Reservoir and the southern Han Reservoir. We chose a district in downstream zone. There5-8sampling lands were chose in each district. We divided each sampling land into136m,142m and148m three sections. We studied the soil seed bank, surface soil physical properties, soil chemical properties and standing vegetation in systematic way. The results showed that:(1) total of69species which belonged to28family and57genera were detected in the soil of water-level-fluctuation zone. Most of them belonged to the main families Gramineae Compositae Cyperaceae and Scrophulariaceae. There was no common dominant species between upstream and downstream districts. The seed density of districts order from high to low was downstream district (5569.2seed per m2), the district between Dan and Han Reservoir (3114.9seed per m2), the southern Han Reservoir (1495.2seed per m2), Dan Reservoir (960.0seed per m2) and the northern Han Reservoir (957.1seed per m2). There was no signification difference among upstream districts. There were significant difference between downstream district and upstream districts. Soil seed density decreased with soil depth. The5biological diversity indexes of downstream district were better than upstream districts. The similarity indexes between Dan Reservoir and the other3upstream districts were from50%to60%. The similarity indexes among the3upstream districts were more than70%. But the similarity indexes between downstream district and upstream districts were less than50%. The life form of soil seed bank species were annual (66.67%) and perennial (33.33%) herbage species.(2) A total of88species which belonged to28family and70genera were found in water-level-fluctuation zone surface vegetation. The dominant families were Compositae, Gramineae, Chenopodiaceae, Leguminosae and Rosaceae. The dominant species were Cynodon dactylon, Polygonum aviculare, Abutilon theophrasti, Potentilla supina and Chenopodium serotinum. The annual herbage and perennial herbage accounted for55.68%and44.32%respectively. A total of59species which belonged to23family and48genera were found in middle section surface vegetation. The dominant species were Cynodon dactylon, Polygonum aviculare, Abutilon theophrasti and Potentilla supine. A total of85species which belonged to28family and67genera were found in up section surface vegetation. The dominant species were Cynodon dactylon, Polygonum aviculare, Abutilon theophrasti and Chenopodium serotinum. There was no obvious difference between middle and up sections. The4biological diversity indexes of up section were better than middle section in upstream districts. The Simpson similarity index and Margalef abundance index displayed common variation trend, and the order from high to low was Dan Reservoir, the southern Han Reservoir, the district between Dan and Han Reservoir and the northern Han Reservoir. The Shannon-Wiener similarity index and Pielou evenness index abundance index displayed common variation trend, and the order from high to low was Dan Reservoir, the district between Dan and Han Reservoir, the southern Han Reservoir and the northern Han Reservoir.(3) In different sections, the longer flooded time is, the higher the soil moisture content is. With the elevation gradient increases, the soil bulk density and soil porosity did not display the same variation trend, and they had obvious difference between different districts. In different sections, the longer flooded time was, the higher the soil ammonium nitrogen and pH was. With the elevation gradient increases, the soil nitrate nitrogen and soil organic matter increased in the middle district, but decreased in the other three districts.(4) The analysis showed significant negative correlation between soil seed bank density and soil bulk density, significant correlation between soil seed bank density and maximum water holding capacity, capillary water holding capacity, minimum water holding capacity, non-capillary porosity, soil organic matter. The similarity indexes between soil seed bank and surface vegetation were0.329in middle section and0.261in up section. The common dominant species between soil seed bank and surface vegetation were Cynodon dactylon, Potentilla supina, Polygonum aviculare, Rumex dentatus and Phalaris arundinacea. Most of them were annual herbage and only Cynodon dactylon was perennial herbage.