Redox properties rhizosphere

The major soil properties that contribute to the changes in copper availability are pH, redox potential, DOC (including root exudates as chelates) and microbial activity (Horak, 1982 Hamon et al., 1995 Marschner and Rdmheld, 1996). To monitor the change in these properties during cultivation, the differences in levels of pH, Eh, DOC and MBM in rhizosphere and bulk soils were measured, and are depicted in Fig. 5. 

The overall effect of plant-microbe interaction shows an increase in MBM in the rhizosphere, owing to the high supply of organic carbon by roots (Lynch and Whipps, 1990). As shown in Fig. 5, enhanced microbial activity was manifested by a steady increase in MBM. Horak (1982) demonstrated that mobilization of copper in the rhizosphere of peas should be a direct outcome of low-molecular-weight root exudates and of an indirect effect via microbial activity in the rhizosphere. The results of the present study show that changes in the major soil properties, including redox potential, DOC and microbial activities, are all in favor of a transformation of metals from less available to more available fractions, leading to variations in various metal fractions in the maize rhizosphere. 

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