Simulating Study On Physiological Response Of Zizania Latifolia To Aeration And Ammonia Nitrogen Stress And Its Nitrogen-denitrification Ability

The degree of eutrophication of water is becoming more and more serious,which has become one of the most important problems to affecting global ecology,human health and sustainable economic development.On the basis of controlling sewage discharge,the method of treating sewage with ecological and biological measures is considered to be effective.At the same time,eutrophication water is usually accompanied by black and odorous phenomenon,the lack of dissolved oxygen is the main reason for this phenomenon,aeration is an effective way to recuperate urban river.In addition,it is of great significance to study the physiological response of aquatic plants in different degrees of polluted water body and take appropriate methods to improve their tolerance to sewage.In this paper,water bamboo?Zizania latifolia?,which is a common emergent aquatic plant in urban polluted water in Shanghai,China,was selected as the target plant.To investigate the removal capacity and some physiological characteristics of total nitrogen?TN?and ammonia nitrogen?NH₄⁺-N?in water under different concentrations of NH₄⁺-N.At the same time,aeration factors were added to study the effect of aeration on ammonia nitrogen conversion,nitrogen removal,the relationship between aeration and plant physiological response,and the combined effect of plant factors and aeration factors on the removal of TN and NH₄⁺-N in water.the results showed that:?1?Water bamboo shoot is an excellent NH₄⁺-N removal plant.Under the condition of no aeration,when the concentrations of NH₄⁺-N was 10 mg/L,50 mg/L,150 mg/L,TN removal was 85.3%,88.0%,67.8%in the plant group,48.5%,35.7%,26.0%in the non-plant group,the NH₄⁺-N removal rate was 93.8%,91.6%,86.1%in the plant group,63.9%,64.1%,48.1%in the non-plant group,respectively.Under condition of aeration,when NH₄⁺-N concentration was 10 mg/L,50 mg/L,150 mg/L,TN removal rates were 85.9%,93.5%,75.0%respectively in the plant group,51.6%,49.0%and 40.3%respectively in the non-plant group.The NH₄⁺-N removal rate was93.9%,96.3%and 92.2%respectively in the plant group,and 65.1%,81.5%,75.5%respectively in the non-plant group,showing a trend of increasing first and then decreasing.Compared with the TN and NH₄⁺-N concentrations in the water of the no plant treatment group in the constructed wetland,the TN and NH₄⁺-N concentrations in water were significantly reduced in the plant groups?p<0.05?.?2?Under the condition that NH₄⁺-N concentration is 10 mg/L,there is no significant difference in the removal effect of TN and NH₄⁺-N in the plant group with or without aeration.In contrast,under medium and high NH₄⁺-N concentrations,TN removal rates in the plant with aeration group were 93.5%and 75.0%,respectively,in the plant without aeration group were 88.0%and 67.8%,respectively.The conversion rates of NH₄⁺-N in the plant with aeration group were 96.3%and 92.2%respectively,and those in the plant without aeration group were 91.6%and 86.1%respectively.That is,aeration in the plant group at medium and high NH₄⁺-N concentrations significantly promoted NH₄⁺-N conversion and TN removal compared with non-aeration?p<0.05?,and improved the purification effect of sewage.?3?The physiological response of plants under low concentration of NH₄⁺-N was not significant.At the concentration of NH₄⁺-N at 50 mg/L and 150 mg/L,the activity of catalase?CAT?and peroxidase?POD?peaked at the second week,solstice.The activity of superoxide dismutase?SOD?peaked at solstice on the third week,,and the activity of POD and CAT was much higher than that of SOD,indicating that POD and CAT were more sensitive to the concentration of NH₄⁺-N in the antioxidant enzyme system of water shoot,and played an important role under the stress of NH₄⁺-N.Under the condition of 50 mg/L NH₄⁺-N concentration,the antioxidant enzyme activity and MDA content of plants can finally be restored to the initial value.At the maximum concentration of NH₄⁺-N 150 mg/L,the final recovery value of antioxidant enzyme activity and MDA content of plants was higher than the initial value,indicating that water conditions at the end of the experiment still had a stress on plants,but plants had certain resistance and adaptability,and the antioxidant enzyme system remained active,that is,150 mg/L concentration of NH₄⁺-N was still within its tolerance range.?4?Under the condition of NH₄⁺-N concentration of 10mg/L,there was no significant change in physiological response of plants with or without aeration.Under medium and high concentration of NH₄⁺-N,aeration plant set of superoxide dismutase?SOD?,peroxidase?POD?,catalase?CAT?activity,malondialdehyde?MDA?content were lower than no aeration group,shows that the water aeration root caused no damage to the plant,it has promoted the transformation of NH₄⁺-N in water,which reduces the NH₄⁺-N of plant stress effect,this result is consistent with the apparent plants for water purification effect.In conclusion,the results of this study show that,when the concentration of NH₄⁺-N is 10 mg/L,whether or not aeration has little significance for the purification effect of plants on water.However,under the conditions of 50 mg/L and 150 mg/L concentration of NH₄⁺-N,aeration can effectively improve the purification effect of plants on polluted water.From micro,under medium and high concentration of NH₄⁺-N,under the condition of aeration group plant antioxidant enzyme activity and MDA content were lower than no aeration group,shows that aeration promoted the transformation of NH₄⁺-N and reduced the stress of NH₄⁺-N on plants.Under the condition of 150 mg/L concentration of NH₄⁺-N,the antioxidant enzyme system of plants still remained active.It also showed that water bamboo had a strong tolerance to NH₄⁺-N and was an ideal plant for the treatment of wastewater with high NH₄⁺-N in artificial wetlands.