Researchs On The Relationships Between Periphytic Algae, Phytoplankton And Vallisneria Natans

Periphytic algae play an important role in aquatic ecosystems and occupied uniqueecological niche. Periphytic algae community has high primary productivity and could be used as food source for various aquatic animals, it also can in-fluence nutrient content in water by different way. Periphytic algae which growth on the surface of large submersed macrophytes can influence the distribution of submersed macrophytes.Submerged macrophyte is an mportant component of plant community in ecological ditches, it can restrain the growth of phytoplankton by nutrient competition and released allelochemicals. But the exorbitant phytoplankton biomass can also influence the growth of submerged macrophytes. In order to study the interactions between periphytic algae, phytoplankton and Vallisneria natans, the research contents are as follows.1. In order to study the effects of nutritional condition on the growth of submersed macrophytes and epiphytic algae. An experiment was carried out over42days in four different nutritional conditions with Vallisneria natans. The results showed that the relative growth rate, superoxide dismutase activity, malondialdehyde contents and epiphytic algae biomass of Vallisneria natans in mesotrophic and eutrophic group was significant different with it in oligotrophic and hypertrophic group (p<0.05). The total soluble sugar content of Vallisneria natans in oligotrophic group was significant higher than other groups (p<0.05). The soluble protein, nitrogen and phosphorus content of Vallisneria natans was significant positive correlation with water nutritional condition. The soluble protein, nitrogen and phosphorus content of Vallisneria natans in oligotrophic and mesotrophic group was significant different with it in eutrophic and hypertrophic group (p<0.05). The chlorophyll a content of water column in different groups does’t exist significant differences. It is therefore concluded that the middle nutritional condition (TN=0.8mg/L, TP=0.08mg/L) was most suitable for the growth of Vallisneria natans and the biomass of periphytic algae was lower. 2. In oder to study the effect of periphytic algae on nitrogen and phosphorous concentration. An experiment was carried out over12days with periphytic algae on artificial material. The results showed that the biomass of periphytic algae in different groups all have increased with varying degrees. The periphytic algae showed prominent removal capability to total nitrogen, ammonium nitrogen, nitrate nitrogen, soluble phosphate and total phosphorus. The periphytic algae have also increased the DO content in water. At the end of this experiment, the cumulative removal rate of total nitrogen, ammonium nitrogen and nitrate nitrogen can get above70%,90%and50%. The cumulative removal rate of soluble phosphate and total phosphorus based on the second day in different groups can also get above50%.3. In oder to study the phytoplankton removal capability of Vallisneria natans. A microcosm ecosystem was set up with Vallisneria natans and examing the changes of Chl-a and biomass of Vallisneria natans in different groups. The results showed that the high density Chl-a content had obviously declined, but the Chl-a content in blank control had obviously increased, but the Chl-a content in Vallisneria natans control always maintained at a low level. At the end of experiment, the Chl-a content in blank control was significant higher than other groups (p<0.05), but the Chl-a content in treatment group and Vallisneria natans control had no significant differences (p>0.05). The change of biomass of Vallisneria natans showed that the influence of high density phytoplankton on Vallisneria natans was remarkable. The underwater light intensity and DO content was closely related to the change of phytoplankton biomass.