Effects of farming on wetland soil seed banks in the Sanjing Plain and wetland restoration potential
农田开垦对三江平原湿地土壤种子库影响及湿地恢复潜力

Seed banks are an important source of regenerative material in wentlands, and can be of value in the restoration of farmed wetlands if the seeds can survive periods of cultivation. A seed bank assay was performed in a greenhouse under two water regimes to evaluate the community structure of the soil seed bank of natural versus farmed wetlands for different years in the Sanjiang Plain of northeastern China. The seeds of fifty plant species germinated from the seed bank. The number of species germinated from seed banks decreased gradually with the increase of the farm years, which were 34, 31, 21, 21 and 8 in natural wetland and farmed wetlands for 1yr, 3yrs, 10yrs and 20yrs respectively. One-way ANOVA was performed and showed that mean species richness and seedling density of seed banks have significant difference among habitats(F1=8.32,F2=5.946,P<0.001).The seed density of the natural wetland and wetland farmed for 1yr were 7624 individuals/m2, 9836 individuals/m2, much higher than that in wetlands farmed for 3yrs and 10yrs, whose seed density were 4336individuals/m2, 4872individuals/m2 respectively. The lowest of seed density occurred in wetland farmed for 20yrs, which was only 432 individuals/m2. The number of species and seedling density of seed banks under drawdown condition were significantly higher than that under flooded condition. Seed density varied with depth so that seed density was higher in 0-5cm than in 5-10cm. Calamagrostis angustifolia, the dominant species in the vegetation of the Sanjiang Plain had 1192 individuals/m2 germinating in the seed bank from the natural wetland; this species was absent in seed banks after 20 years of farming. Our research suggests that even after several years of farming that these wetlands retain the seeds of many species, which can be valuable for wetland restoration.