Speciation and Biochemical Transformations of Sulfur and Copper in Rice Rhizosphere and Bulk Soil-XANES Evidence of Sulfur and Copper Associations

The speciation of sulfur and copper in rice rhizosphere and bulk soil was investigated using integrated approach including sequential extraction and X-ray absorption near edge spectroscopy (XANES). Our results showed that Cu speciation exhibited a difference in rhizosphere and bulk soil of rice. In a flooded paddy soil, most Cu in the rhizosphere existed as Cu (II), whereas part of Cu transformed to Cu (I) in the bulk soil. Sulfur XANES showed the presence of multiple both oxidized and reduced states of sulfur in studied soil samples, with more oxidized sulfur in the rhizosphere than in the bulk soil. Copper and sulfur speciation changed depending on redox conditions. Changes in redox potential and microbial action shifted the sulfur oxidation and reduction reaction and affected the Cu speciation. Sulfur transformation played an important role on Cu speciation.