Decomposition Processes Of Several Submerged Plants

Eutrophication of water bodies has become the major environmental problems in the world today. As the important part of the ecosystem, aquatic plant is not only a primary producer in the food chain, but also plays a major role in lake nutrient accumulation and circulation. The decomposition of aquatic plants is a key step to nutrient cycle and energy flow in lake, and a main process of maintaining the lake ecosystem functions. Studying decomposition processes and nutrient dynamics of submerged plants was of great importance for understanding of material cycles in aquatic ecosystems. Studies of decomposition processes of aquatic plants have been focused on emergent macrophyte. Much less attention has been paid to decomposition processes of submerged plants.In this paper, two submerged plants (i.e., Potamogeton crispus L. and Potamogeon pectinatus L.) in Darning Lake and four submerged plants (i.e., Potamogeton lucens L., Potamogeton cristatus, Ceratophyllum demersum L. and Myriophyllum spicatum L.) in Nansi Lake were collected as the experimental materials, the decomposition processes and nutrient dynamics of submerged plants were investigated for 60 days under different biomass densities and temperatures, and laboratory simulated conditions, using the mesh bag method. The results showed:The decomposition rates of submerged plants were very fast. The decomposition process showed that the decomposition rates were faster in early stage than in later stage for submerged plants. There were some relationships between decomposition rates and biomass densities. The decomposition rates of P. pectinatus decreased with the increase of biomass densities during the whole decomposition stage. The decomposition rates of P. crispus increased with the increase of biomass densities in the early stage and decreased with the increase of biomass densities in the later stage.There was no significant correlation among contents of TOC, TN, TP in residuals of submerged plants and biomass densities in decomposition process. Changes of carbon contents were gently during the whole decomposition processes. In early stage of decomposition, variation tends of nitrogen in different plants’residues were different, while in later stage, the nitrogen contents of submerged plants settled out. Phosphorus contents in stem and leaves of submerged plants were quickly decreased during the early decomposition period.The substrate quality of submerged plants had essential effects on decomposition rate. Correlation analyses indicated that the decomposition rates were positively correlated with the initial nitrogen and phosphorus contents of submerged plants, and were negatively correlated with the crude fiber contents and C/N, C/P in submerged plants.Decomposition processes of submerged plants were influenced by multiple factors. Temperature was the main factor influencing the decomposition rates of submerged plants. The difference of dry mass remaining rate was tested on submerged plants under different temperatures. The results show that the effects of temperatures on decomposition processes primarily occurred in the early decomposition stage whereas the effects on dry mass remaining rate in the later stage were negligible.The higher temperature significantly accelerated the decomposition rate in the early stage for submerged plants, but did not increase the final decomposition efficiency for submerged plants. The substrate quality of submerged plants is the essential factor influencing the decomposition processes. The final decomposition efficiency for submerged plants depends on the proportions of difficult decomposable materials in residues.Temperature had been influenced the nutrient release during the decomposition. The lower temperature accelerated the nutrient accumulations in residues of submerged plants.