Effects Of Modified Biochar On Cadmium And Arsenic Bioavailability And Rhizosphere Microecology In Paddy Soil

Recent years,soil heavy metal pollution has become one of the most serious and widespread environmental problem,about 150 million acre of heavy metal contaminated soil,the proportion of mild pollution is high in China.Due farmland limitation,the technique of lay fallow can not be adopted,in-situ passivation as an effective soil heavy metal pollution remediation technology,attracting widespread concern due to its simple,fast and low-cost features.The yield per unit area of grain(rice)can be increased by more than 10% after the restoration of farmland soil for moderate and slight pollution,and the soil after restoration has great utilization value.In this paper,the cadmium and arsenic contaminated agriculture soil is the main research object.We prepared a pair of modified biochar(ABC/NZVI)which can effective remove Cd(II),Cu(II),Ni(II)and Cr(VI),and the effects of ABC/NZVI on the cadmium and arsenic in soil was studied by pot experiment in greenhouse.The effects of modified biochar on the cadmium and arsenic speciations and the uptake of cadmium and arsenic in different stages of rice growth(Tillering,Booting,Flowering and Ripening)were analyzed.The main results are as follows:1.Modified biochar could improve soil pH,decrease the available content of cadmium in the soil,promote the transformation of cadmium to the residual,and reduce the accumulation of cadmium in rice.At the same time,the addition of modified biochar can reduce the enrichment of arsenic in rice plants.Although,the effect of modified biochar on arsenic formation in soil is weak,but it can reduce arsenic content in rice,The content of arsenic in stem decreased by 47.8%,which indicated that the enrichment of heavy metals in rice was not only related to the soil heavy metal morphology,but also closely related to the iron plaque on rice root,which may promote formation of iron plaque and then it reduce the ability of cadmium and arsenic migrate to the upper part of the plant,result in cadmium and arsenic decreased in rice.2.The addition of modified biochar increased available nitrogen in paddy soil by 1.5% in tillering and 1.7% in maturity,while the nitrogen content of stem and grain increased by 47.2% and 42.1% respectively.Differences of ? and ? diversity indices in the same treatment at the tillering and maturity were significant,indicating that microbial community of rice rhizosphere will change with the growth period.Modified biochar had a great influence on the relative abundance of specific population of microbial communities.While differences between the relative abundance of the microbes in the same period was significantly.Compared with the control group,the Geobacter abundance of the modified biochar was increased by 175%,Nitrososphaera decreased by 61% and 33% at tillering and maturity stages,respectively.As Nitrososphaera belongs to ammonia oxidizing related microorganisms,there may be a relationship between the inhibition of Nitrososphaera and available nitrogen and rice tissue nitrogen increased by the addition of modified biochar.In addition,modified biochar can also affect other physical and chemical factors,which can change certain physicochemical properties of soil and improve the rhizosphere environment of rice,especially in improving the utilization of nitrogen in soil.