Changes of biomass and nitrogen content of the reed (Phragmites communis) under different soil moisture conditions in the hydro-fluctuation belt of the Three Gorges Reservoir

After researching the soil moisture contents of the hydro—fluctuation belt in the Three Gorges Reservoir Area,three different water treatments were applied to the reed(Phragmites communis) to determine the changes of nitrogen and aboveground biomass. The treatments T1(with soil completely submerged under 2 cm of water) ,T2(with soil water content 70% to 100% of field capacity) ,and T3(with soil water content 40% to 60% of field capacity) simulated the conditions in the hydro-fluctuation belt. In all three treatments,nitrogen content and the aboveground biomass of P. communis showed single-peak curves corresponding to seasonal changes. The maximum nitrogen content in leaf and leafstalk of all three treatments appeared in late September;N values in leaf were 23.1、26.5 and 26.2 mg·g-1,and in leafstalk were 14.4、12.4 and 13.2 mg·g-1 respectively,but the contents of nitrogen in the stem of P. communis reached peak values of 9.5、9.1 and 9.0 mg·g-1 in late October. Compared to reeds in other areas,P. communis is known to have a higher water absorption capacity. The aboveground biomass in treatments T1 and T2 was largest in late September:11.86 g per plant and 11.81 g per plant,respectively,but for T3 biomass was largest in late August,at 8.04 g per plant. The nitrogen accumulation in the whole plant also peaked in late September for T1 and T2,at 241.9 mg per plant and 279.4 mg per plant respectively,but T3 peaked in late August at 154.5 mg per plant. This indicated that these plants had the best accumulative ability of nitrogen in the hydro-fluctuation belt in the Three Gorges Reservoir Area. It was also demonstrated that P. communis could not only absorb nitrogen well but also had better N accumulation ability. In addition,according to the growth and nitrogen accumulation of P. communis,we can ensure the best harvest time to reduce the content of nitrogen in the area. Therefore,P. communis could be a precedent species for restoration and rehabilitation of vegetation in the hydro-fluctuation belt of the region around the Three Gorges reservoir.