Changes Of Nitrogen Stable Isotopes In Ulva Pertusa Under Different Nitrogen Sources

As a very common large marine algae,Ulva pertusa has important ecological significance and is often used as a raw material for processing food or feed,or to purify the water quality of aquaculture water.In this experiment,the absorption of different inorganic nitrogen sources by Ulva pertusa,a large marine algae,was studied,which provided a scientific basis for the purification of aquaculture wastewater by using the pores.The test method of this study was to add three different inorganic nitrogen sources,such as ammonium chloride,sodium nitrate and sodium nitrite,and set four different initial concentrations,data were measured at certain time intervals.At the same time,potassium dihydrogen phosphate reagent(KH2PO4)is added as a phosphorus source,and CO2 dissolved in water in the outside atmosphere is used as a carbon source.The measured indicators are:the concentration of ammonium nitrogen(NH4+-N),nitrate nitrogen(NO3--N),nitrous oxide(NO2-N)in the water,the content of chlorophyll a in Ulva pertusa,and the carbon stable isotope(?13C)and nitrogen stable isotope(?15N)of Ulva pertusa.It can be seen from the change of nitrogen nutrient concentration in water body that the three nitrogen sources of NH4+,NO3-and NO2-can reach the ideal removal rate,which are 88%?91%,81.06%?90.84%and 73.35%?88.77%,respectively.In the group with ammonium chloride as the sole nitrogen source,the concentration of NH4 decreased,but the concentrations of NO2-and NO3-increased.In the group with sodium nitrate as the sole nitrogen source,the concentration of NO3-decreased,and the concentration of NH4 decreased,but the concentration of NO2-increased;in the group with sodium nitrite as the sole nitrogen source,the concentration of NO2-decreased,the concentration of NH4 remained basically unchanged,but the concentration of NO3-increased.It can be seen from the change of chlorophyll a content that chlorophyll a is synthesized faster in the early stage of experiment and slower in the latter part of the experiment.After absorbing the nitrogen sources of NH4+,NO3-and NO2-,the chlorophyll a content was increased by 60.53%?64.44%,51.25%?58.21%,and 48.38%?59.47%,respectively.It can be seen from the change of ?15N of the Ulva pertusa,at the beginning of the experiment,the 15N of the Ulva pertusa drastically decreased rapidly,and then decreased slowly or substantially unchanged,and increased slightly in the later stage of the experiment.And the higher the concentration of nitrogen source,the more obvious the decrease of ?15N.It can be seen from the change of ?13C of Ulva pertusa that the 513C of Ulva pertusa decreased significantly at the beginning of the experiment,and the fluctuation of ?13C increased in the later stage of the experiment.In summary,Ulva pertusa has a good absorption effect on inorganic nitrogen,which can meet the needs of its own growth and reduce the concentration of inorganic nitrogen in the water.Therefore,the use of Ulva pertusa in the purification and treatment of aquaculture water has good development prospects.