Attachment Relationship Between Algae And Water Nutrients And The Decline Of Submerged Plants

On the surface of submerged plant, there is usually a periphyton layer with complex composition, including algae, organic matter, sediment, zoogloea, etc. Numerous studies have showed that periphyton has a significant effect on submerged plant’s growth and the main mechanism maybe limiting available light radiate of submerged plant. According to the studies of the relationship between periphyton and submerged plant under different nutrient levels, it can be concluded that the biomass of periphyton increases and the effect of periphyton’s photoinhibition on submerged plant more significant along with the increase of nutrient concentration in water body, therefore, nutrient concentration plays an important role in the effect of periphyton on submerged plant.Vallisneria nantans and Potamogeton crispus, the dominant submerged-plant species of the middle-lower reaches of the Yangtze river, were used as the experimental material in the research, the relationship between submerged plant and periphyton as well as the effect of periphyton on P. crispus in decline phase are discussed through investigating the biomass and specific composition of periphyton that attached on submerged plants’leaves under different nutrient levels. The conclusions are as follows:(1) All periphyton species observed in the lab simulation research under different water nutrient levels belongs to35Species,32genera and5Phyla among which Chlorophyta occupies the most including17species,15genera. There is a significant correlation between periphyton’s biomass and TN, TP in the water, which proved that the growth of epiphytic algae was promoted by high nutrient level in water, while the growth of submerged mycrophytes inhibited.(2) All periphyton observed in the research of periphyton species that attached to the leaves of V. nantans in rivers belongs to32species,27genera,5phyla. Chlorophyta with17species,13genera comprises the most and also occupies the most dominant species. Significant correlation was observed between periphyton biomass and TP in water.(3) All periphyton observed in the research of periphyton species that attached to the leaves of P. crispus in ponds belongs to34species,31genera,5phyla. Chlorophyta contributes the most including15species,13genera. Bacillariophyphyta occupied the most dominant species. Significant correlation was indicated between periphyton’s Chl.a content and TP in water, highly significant correlation was observed between periphyton cell number and N/P in water, while no correlation between periphyton’s organic matter and nutrient level in water.(4) The research of periphyton species on the leaves of P. crispus in decline phase revealed that water quality may be the main reason that caused the correlation trend between the periphyton’s biomass and the decay degree of submerged mycrophytes, that is, periphyton’s biomass increased with the speeding up of decline degree of submerged mycrophytes in high pollution water, while decreased in low pollution water.