Study On The Migration Of As And P In The Avicennia Marina-Soil System Under P And As Interaction

Mangroves are woody plants which occur in the tropical and subtropical estuaries,it has a very high economic and ecological value.In recent years,As has been used extensively in industrial and agricultural production activities.Due to the indiscriminate discharge of arsenic waste water,which results in the enrichment of As in mangrove sediments.As a result,the pollution in the mangrove is becoming more and more serious.As concerns for arsenic can pass through the food chain and pose a threat to human health,therefore it is important to discuss the biogeochemical processes of As in mangrove wetlands.P and As belong to VA,they are not only similar on the physical properties,but also common in plants transport pathway.A large number of studies have shown that there is a significant interaction between As and P in hydrophyte.However,previous studies concerning the reciprocal action of As and P on plant growth and As tolerance in mangroves are limited.Hence,this topic still deserve further study.A sand culture combined with soil culture was used in this experiment to investigate the As and P migration in the Avicennia Marina-Soil system under P and As supply.The indexs of plant biomass,concentrations of As and P,radial oxygen loss(ROL),iron plaque were analyzed to provide theoretical basis for revealing the relationship between heavy metal and source elements.The main conclusions of this study are as follows:1.Sand culture experiment showed that As stress siginificantly affected A.Marina biomass(p<0.001),which represented that biomass was decreased with the increase of As stress degree.ROL of A.Marina is inhibited by the addition of As(p<0.001).The concentration of As treatment had a significant effect on the contents of As in the A.Marina(p<0.001).As content followed the order of root>stem>leaf.The addition of Fe and As can facilitate the formation of iron plaque which will increased the adsorption of As in the solution.2.The total biomass increases with the rise of P(p<0.001).ROL of A.Marina is inhibited by the addition of P(p<0.001).The supply of P in the nutrient solution significantly reduces the amount of As in plant,it shows that P addition suppressed the absorption of As in A.Marina.3.Rhizosphere simulation experiment showed that the content of As in root,stem and leaf of A.Marina was increased with As supply,show the following trend:root>stem>leaf.Adding P promoted the roots to absorb of As,this is probably because As on the soil particles be substituted by P and released into the soil solution,so the As concentration is increased with the addition of P.The content of iron plaque-Fe and iron plaque-As in A.Marina roots increased with the rise of As concentration in sediment.Iron plaque-Fe and iron plaque-As had significant positive correlation(r=0.823,n=45,p<0.001).4.The comparison of sediment rhizosphere and non-rhizosphere showed that:there is no significant difference of pH under As and P treatment,but the rhizosphere pH is significantly lower than the non-rhizosphere the pH(t=-11.009,df=44,p<0.001);The content of As in rhizosphere and non-rhizosphere of A.Marina was increased with the As supply and the As content in the rhizosphere soil is significantly higher than non-rhizosphere soil(t=8.117,df=44,p<0.001).For both rhizosphere soil and non-rhizosphere soil,the applying of P reduced the content of As.5.Inorganic phosphorus grading extraction results showd that whether it's in the rhizosphere soil or in non-rhizosphere soil,Fe-P was the dominant fraction,the following form is Ca-P,then Al-P,the last one is the Ex-P.The content of Fe-P and Ca-P both higher in rhizosphere soil environment that may be attributed to the oxygen released by mangrove roots,this findings also indicate that root activities may play an important role in the aspect of changing the forms of phosphorus.