Effects Of Plants On Soil Environment And Nitrogen Storage Forms In Rainwater-sewage Alternating Biofilte

In recent years,rainwater biofilters have been widely used as a typical urban stormwater management measure to solve urban runoff pollution.As an indispensable element of biofilters,the role of plants is also crucial.In this study,the alternating mode of rainwater and sewage inflow was used to compare the effects of different plants on the environmental factors and the removal of nitrogen and phosphorus pollutants in the biofilters.The effects of plants on the spatial and temporal distribution of nitrogen morphology in the soil of the biofilters were analyzed.In addition,the changes of soil enzyme activity and microbial community differences in the biofilters caused by plants were studied.Finally,the correlation between the dominant microbial flora of biofilter microorganisms planted with different plants and environmental factors,pollutant removal efficiency,nitrogen occurrence morphology,etc.was analyzed.The main conclusions were as follows:（1）Plants had a great influence on the pH,moisture content and conductivity（EC）of the biofilter,the overall pH of the biofilters were weakly acidic,long-term operation would reduce the pH,the pH of the Calamus biofilter was the lowest,and the pH of the plant-free biofilter was above 6.5.The bottom moisture content of different biofilter was greater than that of the surface.The changes in summer and autumn were closer,the difference between the Canna biofilter was the largest,and the Calamus biofilter was the closest.On the contrary,except for the plant-free biofilter,the surface EC of all biofilters was significantly larger than that of the bottom EC,and the changes were stable in summer and autumn,with the mean difference of the bottom EC of the Canna biofilter being the largest and the Iris biofilter being the smallest.（2）Comparing the seasonal effects of different plants on the nitrogen and phosphorus removal performance of the biofilters,it could be found that summer and autumn were more conducive to the biofilter nitrogen and phosphorus removal.The plant effectively improved the nitrogen and phosphorus removal efficiency of the filter.The average removal efficiency of Canna for TN,NH₄⁺-N and NO₃^--N was the highest,reaching 70.80%,79.49%and 82.75%,respectively.The plant-free efficiency was the lowest and the most unstable.Plants mainly participated in the nitrogen cycle of the biofilter tank.The promotion effect on the removal of phosphorus pollution was not obvious.The soil nitrogen morphology content of biofilters planted with different plants was high and increased with the increase of biofilters operation time.The absolute dominant form of no-plant biofilter was carbonate bound nitrogen（CN）.The proportion of no-plant nitrogen morphology was the least affected by the season.In summer and autumn,CN became the dominant form of the remaining four types of plant biofilters,while ion exchange nitrogen（IEN）and iron manganese oxide nitrogen（IMON）would only become dominant forms in spring and winter.Residual nitrogen（RN）was the nitrogen form with the largest increase in Iris biofilter and Calamus biofilter.（3）With the increase of time,the enzyme activity of different plant biofilters first increased and then decreased.The activity in summer and autumn was significantly higher than that in spring and winter.The activity of the middle and lower layers of the biofilter was generally higher than that of the surface layer.In comparison,the total acidity and sucrase activity of Iris were the highest,which could reach 10.69 cmol/kg and 59.43 mg/g·24 h.The activity of Canna urease and nitrate reductase were the highest,which could reach 0.8541 mg/g·24 h and 0.5377 mg/g·24 h.All the indicators of plant-free biofilter were the lowest.For biofilters of different plants,the long-term operation of the biofilters would increase the abundance and diversity of soil microbial community.The Canna biofilter had the highest microbial abundance,with ACE of2043.At the phylum level Proteobateria was the absolute dominant flora of the five biofilters,only 41%of the Calamus and more than 50%of the others.In addition,the correlation between microbial dominant flora and environmental factors was obvious,and the dominant flora also had different effects on the nitrogen and phosphorus removal efficiency of the biofilter and the transformation of soil nitrogen morphology.