Study On P Accumulation And Rhizosphere Soil Properties Of Pilea Sinofasciata In Soil Treated With Optimum Nitrogen

The inappropriate application of phosphate（P）fertilizer and livestock manure in agricultural ecosystem causes P accumulation in soil,leading to eutrophication of waterbody and other environmental problems.High P-accumulating plants can be used to effectively extract the excess P in the environment due to their strong capacity of absorption and accumulation.P accumulation ability and P remediation efficiency of plants could be improved by application of nitrogen（N）fertilizer.However,the mechanism of the effect of N application on P accumulation characteristics in plants was unknown.Pot experiments was conducted to investigate the effect of N application on P removal potential and rhizospheric characteristics of Pilea sinofasciata under high P conditions in this study.A summary of the primary results are as follows:（1）Under the optimum N treatment,with the increasing dose of P application,the biomass and P accumulation of two ecotypes of Pilea sinofasciata were largest at 800 mg kg^-1P application,and then significantly decreased.While the P concentration of Pilea sinofasciata reached the maximum at 1200 mg kg^-1 P application.There was no significant difference in P concentration between the mining ecotype（ME）and the non-mining ecotype（NME）,while the biomass and P accumulation of the ME were significantly higher than those of the NME when P application rate were 400 and 800 mg kg^-1.The maximum shoot biomass and shoot P accumulation in the ME were 27.23g plant^-1 and 193.82 mg plant^-1,respectively,which were 1.18 and 1.24 times higher than those of the NME,indicating that the P accumulation potential of the ME was greater.The P enrichment coefficient of Pilea sinofasciata significantly decreased with the increase of P application rate,but the translocation rate of plant didn’t change significantly.With the increase of P application rate,the P extraction rate and the effective number of whole plant and shoot in two ecotypes of Pilea sinofasciata decreased,while the P removal from soil firstly increased and then decreased,reaching the peak at 800 mg P kg^-1treatment.Except for the treatment without P application,the P extraction rate and P removal from soil of the ME were higher than those of the NME,and the effective number of the ME was lower than that of the NME,indicating that the ME had greater P extraction potential.（2）Compared with the treatment without N application,the optimum N application significantly increased the concentrations of H₂O-P and Na HCO₃-Pi in the rhizosphere soils of two ecotypes of Pilea sinofasciata,and decreased the concentration of Na HCO₃-Po in rhizosphere soil of two ecotypes of Pilea sinofasciata,with no significant effect on the concentrations of Na OH-Pi/Po,HCl-Pi/Po and Residual-P.The concentrations of H₂O-P and Na HCO₃-Pi in the rhizosphere soil of two ecotypes of Pilea sinofasciata were higher than those in the non-rhizosphere soil.With an increase of 10.24%and 20.47%in rhizosphere soil of the ME,14.69%and 16.71%in rhizosphere soil of the NME.The concentrations of Na HCO₃-Po and Na OH-Pi/Po in the rhizosphere were lower than those in the non-rhizosphere soil.There were no differences of HCl-Pi/Po and Residual-P concentrations in the rhizosphere and in the non-rhizosphere.With the optimum N treatment,the concentrations of H₂O-P and Na HCO₃-Pi in the rhizosphere soil of the ME were lower than those of the NME,with took up 90.1%and 81.3%of H₂O-P and Na HCO₃-Pi in the rhizosphere soil of the NME.No significant difference of other P fraction was observed between two ecotypes of Pilea sinofasciata.（3）The acid phosphatase,alkaline phosphatase and phytase activities,the soil microbial biomass C,N content and soil respiration intensity in rhizosphere soils of Pilea sinofasciata were increased by the application of N treatment.N application could significantly increase the activities of soil phosphatase and soil microorganism.The activities of acid phosphatase,alkaline phosphatase,phytase and soil respiration in the rhizosphere soil of two ecotypes of Pilea sinofasciata were significantly higher than those in the non-rhizosphere soil.Under optimum N treatment,the activities of acid phosphatase,alkaline phosphatase and phytase in the rhizosphere soil of the ME were higher than those of the NME,with an increase of 7.50%,15.1%and 8.93%in the rhizosphere soil of the ME,respectively.There was no significant difference in microbial biomass C and N,soil basal respiration and substrate-induced respiration between two ecotypes.Bacteria dominated the microorganisms in rhizosphere and non-rhizosphere soil of Pilea sinofasciata,accounting for 91.8%～96.1%of the total microorganisms.Optimum application of N increased the concentration of bacteria PLFA and decreased the concentration of fungi PLFA in rhizosphere soil of the ME,with an increase of 11.5%and a decrease of 49.7%.N application had little effect on soil microorganism PLFA in rhizosphere soil of the NME.The PLFA of soil microorganism and bacteria in the rhizosphere soil of two ecotypes of Pilea sinofasciata were significantly higher than those in the non-rhizosphere soil,however there was no significant difference in PLFA of soil microorganism and bacteria between two ecotypes of Pilea sinofasciata.（4）The tendency of P fraction and phosphatase activities in the rhizospheric microdomain soil of two ecotypes of P.sinofasciata was similar on the conditions of N application and without N application.Under optimum N treatment,the concentrations of soil H₂O-P and Na HCO₃-Pi were higher in the range of 4mm and 6mm away from root in the ME,and higher in the range of 2mm and 8mm away from root in the NME than those in the non-rhizosphere soil,which showed significant P enrichment in rhizosphere soil.Under optimum N treatment,the concentrations of soil Na HCO₃-Po and Na OH-Pi/Po were lower in the range of 6mm away from roots in two ecotypes of P.sinofasciata than those in the non-rhizosphere soil,which showed significant P wane in rhizosphere soil.No significant difference was observed of concentrations of soil HCl-Pi/Po and Residual-P in the rhizospheric microdomain soil.Thus,P.sinofasciata could make use of soil P in the range of 6mm away from root.The activities of acid phosphatase and alkaline phosphatase in soil within 4mm from the root in two ecotypes were significantly higher than those in non-rhizosphere soil,and the activity of phytase was higher within 8mm.The ME had higher activity of alkaline phosphatase in the rhizospheric microdomain soil than the NME,which was beneficial to promote the mineralization and hydrolysis of organic P（Po）in rhizosphere soil of the ME.（5）On the condition of optimum N application,no significant difference was observed in the diversity of the soil bacterial community within the range of 8 mm in the rhizosphere microdomain of the ME,and the diversity of the bacterial community in the rhizosphere soil of the NME was lower than that in other microdomain soils.In terms of the composition of soil bacterial community,Proteobacteria,Actinobacteria and Acidobacteria are the three dominant phyla with relatively high abundance in rhizosphere microdomain soil of two ecotype of Pilea sinofasciata,and Firmicutes are the dominant phyla in rhizosphere microdomain of the ME,which play an important role in absorpting and accumulating P of the ME.