Inflence Of The Ratio Of Nitrate To Ammonium Of Nutrients Absorption Of Oenanthe Javanica And Ipomoea Aquatica In Aquaculture Water

It is a win-win development of technology and economy,using aquatic plants to restore polluted water.Growing aquatic plants in aquaculture polluted water with excess N and P nutrition is a safe,low-carbon and sustainable food production mode,also an important development direction of recycling of polluted water in aquaculture.The ratio of nitrate to ammonium（NO₃^--N/NH₄⁺-N）in different types of aquaculture water is different.The plant growth and the removal ability for nitrogen and phosphorus can be directly influenced by NO₃^--N/NH₄⁺-N.The influence of nutrients uptaking in aquatic plants on NO₃^--N/NH₄⁺-N in aquaculture water will provide a theoretical basis for obtaining environmental benefits and economic benefits of aquatic plants in the remediation of aquaculture pollution.In this study,batch hydroponic experiments were conducted to investigate the nutrient removal efficiency,plant growth properties,nitrogen and phosphorus distribution in Oenanthe javanica and Ipomoea aquatica with the ratio of nitrate to ammonium of 14:1,9:1,3:1,1:1 and 1:3,respectively.The hydraulic retention time was 1 d and the growth cycle of two aquatic plants were both 6 weeks.The total nitrogen concentration in the culture of Oenanthe javanica and Ipomoea aquatica was 6 mg/L and 2mg/L,respectively,and the ratio of nitrogen to phosphorus was 6:31 and 2:31,respectively.The correlation analysis of plant growth with nutrient removal efficiency,and NO₃^--N/NH₄⁺-N with accumulation of nitrogen and phosphorus in leaves,stems and roots,respectively,was conducted.In addition,stoichiometric analysis of nitrogen and phosphorus in plants,and the contribution of plant assimilation to phosphorus removal was calculated.Therefore,the influence of plant growth to nitrogen and phosphorus removal and the response mechanism in assimilating nitrogen and phosphorus under different NO₃^--N/NH₄⁺-N were discussed thoroughly.The conclusions were:In terms of water quality purification,when the total nitrogen concentration was 6 mg/L,it was not good for N removal at the ratio of NO₃^--N/NH₄⁺-N 14:1,while had little effect on P removal.When the total nitrogen concentration was 2 mg/L,it was neither favorable to the removal of N and P at 14:1.Plants did not grow well at the ratio of NO₃^--N/NH₄⁺-N 14:1.When the total nitrogen concentration was 6 mg/L,the influence of the ratio of NO₃^--N/NH₄⁺-N on root,stem and leaf growth was significant.The higher ratio was beneficial to the growth of stem and leaf,while the lower ratio was better to the root growth.However,it had little effect on the growth of root,stem and leaf when the total nitrogen concentration was 2 mg/L.In terms of nitrogen and phosphorus accumulation,P absorbed by plants increased more rapidly than N.The accumulation rate of N and P in root of Oenanthe javanica was larger than its stem and leaf when the total nitrogen concentration was 6 mg/L.The accumulation rate of N and P in stem of Ipomoea aquatica was larger than its root and leaf when the total nitrogen concentration was 2 mg/L.The lower ratio of NO₃^--N/NH₄⁺-N was favorable for N accumulation in the root and leaf of Oenanthe javanica.In all,the optimized ratio of nitrate to ammonium was 3:1 for Oenanthe javanica,while 9:1 for Ipomoea aquatica,based on the plant growth and nutrient removal ability.