Abstract:

There is an increasing need to understand the importance of ecosystem services provided by wetlands, including nutrient storage, water quality improvement, soil organic matter enhancement and biodiversity protection. Phragamites australis (common reed) is a dominant plant in many aquatic ecosystems and plays a critical ecosystem service role in wetlands. However, few studies have focused on common reed communities, especially concerning its characteristics in eutrophic wetlands in western China.To investigate the relationship between the biomass of P. australis and the physical and chemical characteristics of water and soil (water depth, N and P water and sediment concentrations, soil organic mater and N and P content of plants), a field study was conducted in September 2002 in Wuliangsuhai, Inner Mongolia where eutrophication is a very serious problem in this arid climate. We randomly selected 15 sampling sites and determined the reed biomass with harvest method in 1 m×1 m plots. To eliminate the effects of different aged stands on biomass, we chose uniform plots of two-year old reed stands. The reed height, culm diameter and the number of shoots were measured and soil, water and plant (leave, stem, rhizome, root) were sampled, and the N and P content analyzed. The results showed that the reed biomass was as high as 1.73-3.00　kg·m2 with a below-ground to above-ground biomass ratio ranging from 1.1-2.1. Many factors influenced reed biomass, but water-depth was the most important factor. Above-ground and above-water biomass increased and the ratio of below- to above- ground biomass decreased with water depth. Water-depth effected reed biomass by changing the morphology and structure of the reed community, such as reed height, culm diameter, density, and biomass allocation. There was a significant correlation between reed biomass and water N concentrations. The nitrogen to phosphorus ratio ranged from 7.59-12.21 (< 14) indicating that N limited the reed growth at the community level. Reed biomass was not correlated with water P concentrations. Soil organic matter did not influence reed biomass because the soil was primarily consisted of mineral and organic sediment with little reed litter that releases phytotoxic acids. To investigate the combined effect of the physical and chemical characteristics of water and soil on reed biomass, an equation was developed which indicated that the reed biomass of Wuliangsuhai was mainly influenced by water depth and N concentrations of the water.