Spatial Distribution Characteristics of Soil Seed Bank in Lower Reaches of Tarim River

Typical severe degradation regions due to irrational utilization of water and land resources in the lower reaches of tarim river were chosen in our study.By using the germination method to experiment on germination of the soil seed bank over two years,the density spatial distribution patterns of the soil seed bank were analyzed.We attempted to research the effect of degradation vegetation on soil seed bank according to the characteristic of potential population in horizontal and vertical distribution.The results show that:(1)the density of the soil seed bank generally ranges from 150 seeds/m2 to 2 300 seeds/m2.In terms of the spatial distribution of the soil seed bank,the changes in the soil seed bank along the riparian and the vertical transects are different with the aggravation in degradation of standing vegetation;(2) the distribution of the soil seed bank in the lower reaches of Tarim river presents similarity to that in desert with the characteristic of block distribution;(3) the condition of microhabitat affects the distribution of the soil seed bank largely,and the density of the soil seed bank in the floodplain is larger.However,in bottomland,tamarisk ramosissima sand-hillock and even grassland with more litter,viable seeds are more than those in bare field and populus forest land;(4) severe degradation of ecology in the lower reaches of Tarim river results in different vertical distribution of the soil seed bank in this region,which is the continually increase in the proportion of upper soil seed bank in the total depth with the aggravation of the degradation of standing vegetation.