Rhizosphere Effects And Mechanisms Of The Removal Of Phosphorus And Heavy Metals By Wetland Plants

Constructed wetland is a new technology for ecological treatment of wastewater.It has been widely used in domestic wastewater treatment,industrial wastewater and mine wastewater treatment.Wetland plants,as an important component of constructed wetlands,play an important role in the removal of pollutants.In the past,the research on rhizosphere of wetland plants mainly concentrated in rice for the production needs,and some studies of wetland plants focused on the relationship between iron plaque formation and nutrient uptake,but there were few studies on on the system research on the wetland plant rhizosphere environment and decontamination function.Therefore,research on the relationship between the rhizosphere and the removal of pollutants could provide theoretical basis for wetland plant species selection,optimization of wetland environmental conditions,improve the efficiency and stability,prolong the operation life of wetland wetland decontamination,and could reveal the way of the removal of phosphorus and heavy metals and rich decontamination mechanism in constructed wetland.According to the availability and the easy cultivation of plant,15 species of wetland plants were collected in Hangzhou,through studing on the root oxidation ability,the root morphology and nutrient absorption ability to screen out the plants with large difference of decontamination ability,physiological and biochemical characters,and sclected as materials to study on the formation mechanism of iron plaque and its adsorption of phosphorus and heavy metals,the absorption and transport function,and rhizosphere biological and microbiological characteristics of wetland plants.The main results are as follows:1.The growth and nutrient uptake characteristics of fifteen wetland speciesAccording to the availability and the easy cultivation of plant,15 species of wetland plants were collected in Hangzhou to study the root oxidation ability,the root morphology and nutrient absorption ability,the results showed that the biomass of 15 wetland plants varied greatly,Canna genralis L.,Typha latifolia L.,Thalia dealbata F.and Lythrum salicaria L.were 4 largest biomass plant.The uptake and accumulation of N and P in the 15 wetland plants under water culture conditions were significantly different.The contents of N and P in plants were significantly correlated with plant biomass,root surface area,root oxidation capacity and so on.he removal rate of NH4+-N,NO3--N and P and the accumulation amount of N,P were higher in C.genralis,T.latifolia,T.orientales and T.dealbata,the purification effect of nutrient pollution in water were obvious.2.Iron plaque formation on wetland plants and its Influence characteristicsFe plaque was induced by adding 200 mg·L-1 Fe2+ as FeSO4.7H2O for 4 days in one set of experiment and 8 days in another.The amounts of iron plaque were higher in Canna.genralis,T.latifolia,T.orientales and T.dealbata,the content of iron plaque of 15 wetland plants were significantly positively correlated with root surface area and root tip number,but not with root oxidative capacity.The amount of Ca,Cu,Zn and P on the iron plaque of the root surface were significantly correlated with the amount of iron plaque treated with exogenous ferrous iron 4 d,it was extremely significantly correlated with the treatment after 8 d.The amounts of iron plaque were higher in Canna.genralis,T.latifolia,T.orientales and L.salicaria,the amounts of Ca,Cu,Zn and P in the Fe plaques and the roots were significantly correlated with Fe plaque amount,but there was no significant correlation with Fe plaques between the amounts of Ca,Cu,Zn and P and the absorption in shoot.3.Effect of Iron Plaque Formation on Phosphorus and Heavy Metal Uptake by Wetland Plantswo kinds of wetland plants(Canna.generalis L.and Cyperus.nutans)were selected to study the effect of Fe amendment in culture solution on Fe plaque formation and accumulation of P,Cu,Cd,Zn and Pb in plant tissues.Fe plaque formation on the roots of wetland plants was influenced both by Fe amendment in culture solution and plant species.Maximum Fe plaque was formed on plant roots at a Fe amendment of 50-80 mg L-1 and C.generalis could form heavier Fe plaques than C.nutans.The content of Pb was the highest in the organs of the two plants of Canna and Cyperus,and the proportion of organelles was the lowest.The content of Pb in cell wall,cytoplas organelles in the root of Canna generalis and Cyperusnutans with iron plaque were smaller than CK,but,the content of Pb in cell wall,cytoplas organelles in the shoot were higher than CK,iron plaque inhibited the absorption of Pb in the root in the two wetland plants and promoted the transfer in shoot.4.Characteristics of rhizoshphere of wetland plants in mimic wastewater treatmentA mimic experiment was carried out to study the microbial quantity,microflora,enzyme activities in the rhizosphere and non-rhizosphere of 4 species wetland plants(Canna generalis,Typha orientalis,Cyperus nutans,Reineckia carned).The results showed that the rhizosphere microbial biomass of the 4 wetland plants was significantly higher than that in the non rhizosphere environment,and the rhizosphere effects were significant.The activities of rhizosphere enzymes in different wetland plants were significantly higher than those in non rhizosphere environments,indicating that rhizosphere effects of wetland plants accelerated the transformation of N and P.The contents of available phosphorus,manganese,copper and zinc in rhizosphere soil of 4 wetland plants were higher than those in non rhizosphere soil,indicating the activation effect of plant roots on these elements.