A Comparative Study On The Decomposition Processes Among Some Aquatic Plants

Wetland litter decomposition is a key step to nutrient cycle and energy flow in wetlands, and a main process of maintaining wetland ecosystem functions, studying decomposition processes and nutrient dynamics of aquatic plants is of great importance for better understanding of material cycles in lake ecosystems. Wetland litter decomposition is influenced by nonbiological factor and biological factor, nonbiological factor means outside environmental condition which acts on the litter decomposition, biological factor includes the phy-chemical property of wetland litter and wetland biota (i.e., heterotrophic microorganism and geobiont). In this paper, six aquatic plants (i.e., Phragmites australis, Zizania latifolia, Nelumbo nucifera, Nymphoides peltatum, Potamogeton crispus and Myriophyllum verticillatum) were chosen as the experimental materials. Under the same external environment conditions such as temperature, moisture and nutrient content, using the mesh bag method, the decomposition processes and nutrient dynamics of the6aquatic plants was investigated in a laboratory environment for64days, and the results showed:(1) The nutriment contents of aquatic plants had some relationship with life form, the sequence of carbon, cellulose, hemicellulose and lignin contents was submerged plants, floating-leaved plants, emerged plants, that of phosphorus contents was emerged plants, floating-leaved plants, submerged plants, and nitrogen contents was floating-leaved plants, emerged plants, submerged plants. While some nutriment of different plants which were the same life form had larger difference, such as the lignin content of Nelumbo nucifera was7.4times larger than Nymphoides peltatum.(2) Substantial differences in decomposition rates were observed among the6plants. The floating-leaved plants presented the highest decomposition rate, followed by the submerged and emerged plants in turn. The decomposition processes had two obvious stages, the decomposition was fast in the early stage, and decreased in the late stage. For each plant, decomposition rate varied by biomass density but had a similar temporal pattern, Phragmites australis, Zizania latifolia and Potamogeton crispus decomposed fastest at the largest biomass density group, Nelumbo nucifera and Nymphoides peltatum decomposed fastest at the least biomass density group, while Myriophyllum verticillatum decomposed fastest at the middle biomass density group.(3) For each plant, nutriment composition of residue varied by biomass density but had a similar temporal pattern. During the decomposition processes, the dynamics of phosphorus, cellulose and lignin contents showed the same variation trend across different plants. Phosphorus contents were decreased substantially in the first4days, followed by a slight increase. Cellulose contents were decreased in the first4days and stabilized afterwards. Lignin contents were increased in the first place and then stabilized. In the early stage of decomposition, variation tends of carbon, nitrogen and hemicellulose contents in different plants’residues were different, while in the late stage of decomposition,the carbon contents of the six plants increased, the nitrogen and hemicellulose contents of the6plants settled out.(4) Correlation analysis of decomposition rates and nutriment contents showed that the decomposition rates tended to be facilitated with increasing initial nitrogen, phosphorus contents; while the rates were slowed with increasing initial cellulose, hemicellulose, lignin contents and C/N, C/P, lignin/N. these initial nitrogen, phosphorus, lignin contents and lignin/N of litter can predict the size relation of different plants’decomposition rates. The main factors affecting the decomposition rates presented a temporal variation. In the early stage of decomposition, decomposition rates tended to be facilitated with increasing hemicellulose contents, C/N, lignin/N; while in the late stage, the rates were slowed with increasing lignin and the other factors played minor roles. This study identified that biomass density had no distinct effect on aquatic plants’ decomposition, by studying the decomposition of six aquatic plants at three biomass density. Correlation analysis of decomposition rates and nutriment contents showed that residue nutriment contents had some influence on residue decomposition rates. The result indicated the rule of residue nutrient releasing the correlation of nutriment content and decomposition rate, could provide a reference for protection on aquatic plants’species selection and community construction in the ecological restoration of the wetland.