title: Mobilization of cadmium by dissolved organic matter in the rhizosphere of hyperaccumulator Sedum alfredii.
abstract: Pot experiments were conducted to investigate the role of dissolved organic matter (DOM) in the Cd speciation in the rhizosphere of hyperaccumulating ecotype (HE) and non-hyperaccumulating ecotype (NHE) of Sedum alfredii and its effects on Cd mobility. After growing HE S. alfredii, the rhizosphere soil solution pH of heavily polluted soil (HPS) and slightly polluted soil (SPS) was reduced by 0.49 and 0.40 units, respectively, due to enhanced DOC derived from root exudation. The total Cd concentration in soil solution decreased significantly but the decrease accounted for less than 1% of the total Cd uptake in the shoots of HE S. alfredii. Visual MINTEQ speciation predicted that Cd-DOM complexes were the dominant Cd species in soil solutions after the growth of S. alfredii for both soils, followed by the free metal Cd(2+) species. However, Cd-DOM complexes fraction in the rhizosphere soil solution of HE S. alfredii (89.1% and 74.6% for HPS and SPS, respectively) were much greater than NHE S. alfredii (82.8% and 64.7% for HPS and SPS, respectively). Resin equilibration experiment results indicated that DOM from the rhizosphere (R-DOM) of both ecotypes of S. alfredii had the ability to form complexes with Cd, whereas the degree of complexation was significantly higher for HE-R-DOM (79-89%) than NHE-R-DOM (63-74%) in the undiluted sample. The addition of HE-R-DOM significantly (P<0.05) increased the solubility of four Cd minerals while NHE-R-DOM was not as effective at the same concentration. It was concluded that DOM in the rhizosphere of hyperaccumulating ecotype of S. alfredii could significantly increase Cd mobility through the formation of soluble DOM-metal complexes.
authors: Ministry of Education, Key Laboratory of Environmental Remediation and Ecological Health, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310058, China. litq@zju.edu.cn
authors: Tingqiang
authors: T
authors: Li
authors: Chengfeng
authors: C
authors: Liang
authors: Xuan
authors: X
authors: Han
authors: Xiaoe
authors: X
authors: Yang
mesh_terms: D001673:Biodegradation, Environmental; D002104:Cadmium / Q000378:metabolism*; D018517:Plant Roots / Q000378:metabolism; D058441:Rhizosphere; D031963:Sedum / Q000254:growth & development / Q000378:metabolism*; D012987:Soil / Q000737:chemistry; D012989:Soil Pollutants / Q000378:metabolism*
chemical_list: D012987:Soil; D012989:Soil Pollutants; D002104:Cadmium