Comparison of speciation and bioavailability of rare earth elements between wet rhizosphere soil and air-dried bulk soil

A comparison was made between the speciation and bioavailability of rare earth elements in rhizosphere and nonrhizosphere soils and between wet and air-dried soils under greenhouse conditions by using a homemade rhizobox. The speciation of rare earth elements in soils is experimentally defined as water soluble, exchangeable and carbonate bound (B1), Fe¯Mn oxide bound (B2) and organic matter and sulfide bound (B3). The air-drying process of the wet soils resulted in an increase in rare earth elements in fractions B1 and B2, and a decrease in B3. Generally, a better correlation was obtained between the speciation and bioavailability by using wet soils than that by using air-dried soils, and as the conditions in the former are close to the realistic conditions of plant growth in the environment better plant availability is also achieved between the speciation of rare earth elements in the rhizosphere soils than that in the nonrhizosphere soils. Application of the rhizosphere wet soils is be strongly recommended in the future study on the speciation analysis and bioavailability of trace elements in soils.