The Influence Of Concentration Of Nitrogen And Phosphorus In Water On Sources Of Nitrogen About Epiphytic Algae

In order to understand nutrient utilization of epiphytic algae and interpret influence mechanism of epiphytic algae on its host plants in eutrophicated lake. Effects of N&P levels in water bodies on epiphytic algae were studied by using conventional laboratory methods combineing with15N stable isotope labeling. Espicallly contents of N&P and the sources of N of epiphytic algae on the surface of the submersed macrophytes (Vallisneria natans) were cared about. The main results were as follows:(1) The biomass, content of N&P and community composition of epiphytic algae changed with increasing levels of N&P in water bodies. The biomass increased with increasing levels of N&P in water bodies during whole culture process. There was a significant positive correlation between biomass and concentration of N&P in water (r=0.652, p<0.01). The N&P concents of epiphytic algae was increasing with the concentration of N&P in water. The N&P concents of epiphytic algae had a significant positive correlation with concentration of N&P in water respectively (rN=0.764,pN<0.01;rp=0.696,pp<0.01). The community composition of epiphytic algae changed with the increasing levels of N&P in water too. In the low concentration of N&P in water (N-P mg/L:0.5-0.05), Navicula was the absolute dominant epiphytic algae genus (38.84%), next were Chlorella (14.08%), Gomphonema (13.57%) and so on. In the high concentration of N&P in water (N-P mg/L:10.0-1.0), Chlorella was the absolute dominant epiphytic algae genus, next were Gomphonema (21.49%), Navicula (15.21%) and so on. The abundance of dominant epiphytic algae was affected by concentration of N&P in water. The abundance of Chlorella and Gomphonema increased with the concentration of N&P in water, whereas the abundance of Navicula decreased.(2) The N in water and the N released from leaves were the N sources about epiphytic algae. The N content and TN content per nuit area of epiphytic algae were increasing with the concentration of N&P in water. The815N and loading15N were decreasing with the increasing levels of N&P in water, but increasing in the high level of N&P. In the same level of N&P in water, when the host plants released more15N, the epiphytic algae could absorbed more N.(3) The concentration of N&P in water, host plants, and the concentration of N&P in sediments had an influence on absorbing15N of epiphytic algae. The concentration of N&P increased in water could help epiphytic algae accumulate more N&P, the N&P concents of epiphytic algae had a significant positive correlation with concentration of N&P in water respectively (rN=0.764,pN<0.01; rp=0.696, pp<0.01). The N&P concents of epiphytic algae was increasing with the concentration of N&P in host plants. The N&P concents of epiphytic algae had a significant positive correlation with concentration of N&P host plants respectively (tN=0.385, PN<0.01; rp=0.506, pp<0.01). In the same level of N&P in water, when the815N, excess15N of leaves and store15N of host plants were high, the815N and excess15N of epiphytic algae were high too. The concentration of N&P in sediments had an indirect influence on absorbing15N of epiphytic algae. In the same level of N&P in water, when the N&P contents in sediment were high, the loading15N of epiphytic algae was high too. When the N&P contents in sediment were exponentially increasing, the loading15N of epiphytic algae was not exponentially increasing.