Rhizosphere iron oxidation

Begg CBM, Kirk GJD, Mackenzie AF, Neue HU. 1994. Root-induced iron oxidation and pH changes in the lowland rice rhizosphere. New Phytologist 128 469-477. 

Kirk GJD, Bajita JB. 1995. Root-induced iron oxidation, pH changes and zinc solubilization in the rhizosphere of lowland rice. New Phytologist 131 129-137. 

In water logged soils radial oxygen loss from the root raises the redox potential in the rhizosphere as a consequence of which iron oxide plaques are seen to develop on root surfaces. Bacha and Hossner (1977) removed the coatings on rice roots growing under anaerobic conditions. The coatings were composed primarily of the iron oxide mineral lepidocrocite (y-FeOOH) as the only crystalline component. St-Cyr and Crowder (1990) studied the iron oxide plaque on roots of Phragmites and detected both Fe and Mn. The Fe Mn ratio of the plaque resembled the ratio of Fe Mn in substrate carbonates. The plaque material also contained Cu. 

Weiss J. V., Emerson D. E., Backer S. M., and Megonigal J. P. (2(X)3) Enumeration of Fe(II)-oxidizing and Fe(III)-reducing bacteria in the root zone of wetland plants implications for a rhizosphere iron cycle. Biogeochemistry 64, 77-96. 

Besides the fluxes of protons that occur to counterbalance charge imbalances, redox-coupled pH changes can also take place in the rhizosphere, as is the case for lowland rice. Kirk and Le Van Du (1997) showed that the precipitation of iron oxide occurring as a consequence of root-induced oxidation of the rhizosphere of rice was responsible for a significant proportion of the concurrent acidification. 

Neubauer, S. C., Emerson, D., and Megonigal, J. P. (2002). Life at tire energetic edge kinetics of circumneutral iron oxidation by lithotrophic iron-oxidizing bacteria isolated from the wetland-plant rhizosphere. Appl. Environ. Microbiol. 68, 3988-3995. 

Oxidized root channels have been observed for few species, including rice (0. saliva), cattails, reeds, Spartina sp., Carex sp., and Potomogeton sp. (see review by Mendelssohn et al., 1995). The iron-em-iched plaques essentially consist of FeOOH minerals (Bacha and Hossner, 1977). Iron plaque may be amorphous or crystalline, in the forms of iron such as ferric hydroxides, goethite, lepidocrocite, and siderite. Iron oxides or hydroxides in rhizosphere have high affinity for metals and metalloids. 

The objective of the present study is to examine the desorption kinetics of Cd following its adsorption on iron oxides. To simulate the effects of organic ligands in soil rhizosphere environment and chloride-bearing fertilizer, Cd desorption caused by citrate, acetate and chloride was investigated. 

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