Microbial transformation rhizosphere

In this chapter I describe how microbial activity may be estimated and what data are presently available on a) rates of microbial transformation and utilization, b) phenolic acid effects on soil and rhizosphere microbial populations, and c) the influences of soil and rhizosphere microbial populations on phenolic acid phytotoxicity. The resulting insight is then used to suggest a possible approach by which this hypothesis may be tested experimentally. 

However, relatively few studies have included growing plants in their experimental systems. In order to mechanistically understand the effects of pine roots on microbial N transformations rates under conditions of N limitation, l-year-old pine seedlings were transplanted into Plexiglas microcosms (121) and grown for 10-12 months. Seedlings were labeled continuously for 5 days with ambient CO concentration (350 iL L ) with a specific activity of 15.8 MBq g C. Then, soils at 0-2 mm (operationally defined as rhizosphere soil) and >5 mm from surface of pine roots (bulk soil) of different morphology and functional type (coarse woody roots of >2 mm diameter fine roots of <2 mm diameter ... 

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 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. 

---