Bioavailability rhizosphere

Phytoremediation in the root zone. Proteins and enzymes produced by the plant can be exuded by the roots into the rhizosphere. These plant products target contaminants in the surrounding soil, leading to precipitation or immobilization in the root zone. This mechanism within phytostabilization may reduce the fraction of the contaminant in the soil that is bioavailable. 

Dissolved organic molecules have many acidic functions (hydroxol and carbonic groups) to complex trace elements and their compounds to form soluble chelates. This is one of the reasons why solubility and bioavailability of trace elements in the rhizosphere are higher than bulk soils. At the same time, many organic acids also directly dissolve trace elements and their compounds in soils. Plant-produced phytosiderophores facilitate elements, such as Fe and Zn, uptake by plants (Zhang et al., 1991 Romheld, 1991 Hopkins et al., 1998). However, Shenker et al. (2001) did not find significant uptake of the Cd-phytosiderophores complex by plant roots. 

Plant roots and root-induced chemical changes in the rhizosphere strongly affect the bioavailability of trace elements (Hinsinger, 1999). First, root-induced changes in the ionic equilibria influence the bioavailability of trace elements. The differential rates of plant uptake of water and ions in the soil solution result in a depletion or an accumulation of the ions in the... 

Hinsinger P. Bioavailability of trace element as related to root-induced chemical changes in the rhizosphere. Proceeding of 5th International Conference on the Biogeochemistry of Trace elements, Vienna, Austria, 1999. 

Hinsinger, P. 2001. Bioavailability of soil inorganic P in the rhizosphere as affected by root-induced chemical changes a review. Plant and Soil 237 173-195. 

It will also be important to understand the rhizosphere ecology around the roots of metal accumulating plants fully. Maximizing the bioavailability of the contaminant metals in this zone may require the optimization of the microbial communities, or perhaps the addition of soil amendments. There are early indications that such intervention may be beneficial (88), but research in this area is at a very early stage. 

Feng, M. H., Shan, X. Q., Zhang, S., and Wen, B. (2005a). A comparison of the rhizosphere-based method with DTPA, EDTA, CaCl2, and NaNC>3 extraction methods for prediction of bioavailability of metals in soil to barley. Environ. Pollut. 137, 231—240. 

Wang, Z.W., Shan, X.Q., and Zhang, S.Z., Comparison between fractionation and bioavailability of trace elements in rhizosphere and bulk soils, Chemosphere, 46, 1163, 2002. 

The phytoremediation process may be viewed as a symbiotic process between plants and soil microbes that involved in phytoremediation (Lasat, 2002). Plant and bacterial interaction can enhance the effectiveness of phytoremediation technology because plants provide carbon and energy sources or root exudates in the rhizosphere that will support microbial community in the degradation and transformation of soil pollutants (Siciliano and Germida, 1998). In addition, the presence of soil microbes can increase the water solubility or bioavailability of pollutants in soils, which facilitates the uptake of pollutants by plants (Lasat, 2002 Siciliano and Germida, 1998). However, the specificity of the plant-bacteria interactions besides being much intricate is dependent upon soil and the aqueous conditions, which can alter contaminant... 

The rhizosphere pH is also of crucial importance for determining the bioavailability of trace elements other than metals. The fate of trace elements that occur as... 

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