Plant and Microbial Uptake

Plant uptake is potentially an important assimilation process for removing organics from wetlands. Few studies have examined plant uptake of toxic organic contaminants. Accumulation of toxic chemicals in biota is usually quantified by a bioconcentration factor (BCF)  

This factor reflects the tendency of a compound to accumulate in plant tissue and is a basis for comparison between different plant species and organic contaminants. 

Most organics can be readily taken up by plant roots and foliage. The chemicals can be transported in living plant tissue (symplast) and nonliving tissue (apoplast). Enzymes in the symplasts may metabolize the chemicals into less toxic compounds. Toxic organics are translocated in cell walls and xylem (apoplast) that form on interconnected continuum within plants. 

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Ronov (1976) estimated the average CaO content in sedimentary layer of 15.91 %, and in granite layer, of 2.71 %. Accordingly, the calcium reservoir in sedimentary shell is 272.8 X 10 - tons, and in the granite pool is 222.8 x lO tons. The weathering and metamorphosis of deep-layer silicates is accompanied by the formation of clay minerals with release of calcium available for plant and microbial uptake. 

The major pools and associated transformations of phosphorus in the soil-plant system are presented in Fig. 13.1. These show that the distribution, dynamics and availability of phosphorus in soil are controlled by a combination of biological, chemical and physical processes. Soil solution is the primary source of phosphorus for plants and microorganisms, and most phosphorus is taken up as phosphate (HPO , H2P0 ). The equilibrium concentration of phosphate present in soil solution is very low (<5 fxM) and phosphate removed by plant and microbial uptake must be continually replenished from the inorganic, organic and microbial phosphorus pools. This is especially important in agroecosystems where demand for phosphorus is high and annual off-farm transfer of phosphorus in produce commonly exceeds 20 kg P/ha (Stevenson and Cole, 1999). 

Iron uptake by bacteria at sites of lateral root emergence has been further confirmed using another technique employing 7-nitrobenz-2-oxa-l,3-diazole-desferrioxamine B, which is a derivitized siderophore that becomes fluorescent after it is deferrated (78). In this case, iron uptake from the siderophore ferrox-amine B was a.ssociated primarily with microbially colonized roots, but both plant and iron uptake from this chelate occurred in the regions just behind the root tips. 

J. Schniirer and T. Rosswall, Mineralization of nitrogen from N-labelled fungi, soil microbial biomass and roots,and its uptake by barley plants. Plant Soil 102 71 (1987). 

E. Bar Ness, Y. Hadar, Y. Chen, and A. Shanzer, Iron uptake by plants from microbial siderophores—a study with 7 nitrobenz-2oxa-1,3-diazole desferrioxamine as fluorescent ferrioxamine B analog. Plant Physiol. 99 1329 (1992). 

Direct uptake by plants and microorganisms. Microbial removal of metals Biological Metals... 

Awad F, Romheld V. Mobilization of heavy metals from contaminated calcareous soils by plant bom, microbial and systhetic chelators and their uptake by wheat plants. J Plant Nutrit 2000a 13 1847-1855. 

Chapman RA, Tolman JH, Cole C. 1994a. The effect of multiple soil applications of disulfoton 011 enhanced microbial degradation in soil and subsequent uptake of insecticidal chemicals by potato plants. J Environ Sci Health Part B Pest Food Contamin Agric 29(3) 485-506. 

Phytoremediation approaches (the use of green plants and their attendant bacteria to remove contaminants from soil and water, either directly by plant uptake or by stimulating microbial activity in the rhizosphere) have attracted interest as a possible low-cost remediation technology (Sadowsky and Smith, 1996). To date the application of phytoremediation strategies to clean up environmental contamination due to 3-triazine herbicides has been limited. However, the uptake and degradation of atrazine by poplar trees has been reported (Burken and Schnoor, 1996,1997). 

The Michaelis-Menten equation is often employed in soil-water systems to describe kinetics of ion uptake by plant roots and microbial cells, as well as microbial degradation-transformation of organics (e.g., pesticides, industrial organics, nitrogen, sulfur, and natural organics) and oxidation or reduction of metals or metalloids. Derivation of the Michaelis-Menten equation(s) is demonstrated below. 

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... 

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