芦苇根孔在湿地生态系统中的动态和功能

The structure and spatial distribution of root channels, the hydrochemistry in the lake (ditch) water and subsurface water within the reed-bed/ditch system, and the matter transport affected by root channels were studied in the land/inland water ecotones with reed domination in Baiyangdian Lake, China..(1) It is found, as the first report, that the root channels formed by hydrophytes thrive in the ecotone soil. According to the statistical results from 17 field profiles, the root channels of reeds are mainly distributed above 120cm along the profile and particularly concentrated at 20-70cm. The area of root channels over 40-60cm section occupies more than 2.2% of the profile section area. The ratios of dead root channels to living ones account for 48.4% and 51.6%, respectively. Over 50% root channels have a diameter of less than 5mm. However, 90% of the root channel area is composed of root channels with diameter of more than 10mm. The wetland root channels spread predominantly along horizontal direction underground. The dye tracer experiment and hydraulic conductivity determination consistently show that the wetland root channels can quickly transport water to far distance within ecotones and consequently provide the transport, adsorption and transformation interface for pollutants such as nitrogen and phosphorus..(2) Field work well verified the new purification mechanism by root channels in the land/inland water ecotone. The purification mechanism of ecotone indicates that the root channels can freely exchange the water between land and water body as far as 4-8 m when the lake water level fluctuates, which considerably increases the purification efficiency by reed bed system. Here the soluble pollutants may be adsorbed or degraded by ecotone soil minerals. The reed-bed/ditch system can achieve best self-purification efficiency at sea level of 8 m. When the lake level rises from 7.3 m to 8.1 m, the concentrations of ammoniacal nitrogen (NH4+-N), total nitrogen (TN), soluble reactive phosphorus (SRP) and total phosphorus (TP) reduce by 90%, 64%, 99%, and 92%, respectively, at 4 m range within reed bed. However, during dry year, the lake level is lower than the root channel zone and only 6.5 m or less, and the purification zone is limited at 0.5 m range at the boundary of reed bed. At sea level of 8 m, the boundary length of effective purification zone in the lake reaches 7670 km and the corresponding effective root channel volume arrives at 9.0×106m3. While at 6.5 m, the length and volume decrease to only 1530 km and 2.8×104m3..(3) The main hydrochemical characteristics of ecotone subsurface water are characterized by high concentrations of CO2, hardness and alkalinity and low dissolved oxygen contents. In the subsurface water of reed beds, the partial CO2 pressure was 23-704 times of that in the atmosphere and the partial O2 pressure was 5-34 % of atmospheric O2 pressure. Root channels of reeds might serve as a unidirectional "CO2 pump" for transporting CO2 into subsurface water. The main ions exhibit spatial gradients from the edge to the center of reed beds. The change of hydrochemical type of the subsurface water occurs at the landward 0.5 m away from the edge of reed bed. The dominant cations in the ditch water and subsurface water are Na+ and Ca2+ respectively. The nutrients in the subsurface water of reed beds maintain low concentrations and vary little with the nutrient level in the lake (ditch) water.(4) The reed bed system, scattered ditches and open lake waters constitute the reed-bed/ditch system in Baiyangdian Lake, in which the reed bed system is composed of reed community, reed-bed soil, and underground root channel system of reeds as trinity. The width of reed beds and shallow ditches is generally 30-40 m and 5-10 m. Within such range of width, wetland root channels are equivalent to "connecting vessels" between reed beds and ditches, thus quickly moving water into the deep side of ecotone. Since multitudinous shallow ditches are connected to watercourses and lakes, this landscape structure significa

本研究拟以白洋淀典型湿地生态系统为研究对象，研究芦苇根在土壤不同深度上的空间分布、径级组成、季节动态以及新老交替规律。同时探讨芦苇根孔在土壤优先水流、溶质传输中的作用。植物根孔的系统研究不仅可以丰富我国在土壤大孔隙和植物根孔方面的研究内容，而且还将为我国利用湿地和生态滤池处理污染水、污泥等新技术提供理论基础。