title: Root-induced changes to cadmium speciation in the rhizosphere of two rice (Oryza sativa L.) genotypes.
abstract: Our aim was to investigate rhizosphere effects on the chemical behavior of Cd. This was done in a glasshouse experiment, where two rice cultivars (Zhenong54 and Sixizhan) were grown in soil spiked with cadmium (Cd) at two levels, 3.9 ± 0.5 and 8.3 ± 0.5 mg kg(-1) soil, placed in a rhizobox until ripening stage. Chemical forms of cadmium near the root surface were then assessed using a sequential extraction procedure (SEP). There were significant differences in Cd species, especially exchangeable Cd (EXC-Cd) between the two rice cultivars as affected by rice roots. The lowest EXC-Cd with Zhenong54 appeared in the near-rhizosphere area with little difference between tillering stage and ripening stage while Sixizhan had its lowest EXC-Cd concentration in the root compartment. Both cultivars had slight changes in the Fe/Mn oxide-bound fraction of Cd (FMO-Cd) at the grain ripening stage while the control treatments without plants had a significant increase in FMO-Cd at the same time, indicating a transformation from a less bioavailable form (FMO-Cd) to more bioavailable forms (EXC-Cd). Soil microbial biomass in the vicinity of the root surface had opposite trends to some extent with EXC-Cd, partly because of the root-induced changes to bioavailable Cd. Unlike Zhenong54, Sixizhan had a higher Cd concentration in the root, but only a small proportion of Cd translocated from the root to grain.
authors.affiliation: Institute of Soil and Water Resources and Environmental Science, Zhejiang University, Hangzhou 310029, China.
authors.forename: Linfei
authors.initials: L
authors.lastname: Hu
authors.forename: Murray B
authors.initials: MB
authors.lastname: McBride
authors.forename: Hao
authors.initials: H
authors.lastname: Cheng
authors.forename: Jianjun
authors.initials: J
authors.lastname: Wu
authors.forename: Jiachun
authors.initials: J
authors.lastname: Shi
authors.forename: Jianming
authors.initials: J
authors.lastname: Xu
authors.forename: Laosheng
authors.initials: L
authors.lastname: Wu
mesh_terms: D002104:Cadmium / Q000737:chemistry* / Q000378:metabolism; D005838:Genotype; D012275:Oryza / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism; D058441:Rhizosphere; D012989:Soil Pollutants / Q000737:chemistry* / Q000378:metabolism
chemical_list: D012989:Soil Pollutants; D002104:Cadmium