Soil bacteria microbial population

Since his early pioneering work on the rhizosphere (a term Hiltner used to describe specifically the interaction between bacteria and legume roots), our knowledge of the subject has greatly increased, and today perhaps a more appropriate definition of the rhizosphere is the field of action or influence of a root (1). The rhizosphere is generally considered to be a narrow zone of soil subject to the influence of living roots, where root exudates stimulate or inhibit microbial populations and their activities. The rhizoplane or root surface also provides a... 

Soil type and structure also influence the dynamics of rhizosphere microbial populations. Whether nutrients are available for bacteria in the rhizosphere often depends on the sites in the soil where nutrients are present. Organic compounds tightly bound to the soil matrix are often less available for bacteria (226), and those present in smaller pore spaces can be physically protected against mineralization. However, disturbance of the soil often cau.ses these nutrients to become more available to soil microbes (227). 

The air that we breathe is full of microbial cells and spores of bacteria and fungi. Because they are extremely light they are readily are carried by wind currents. In hot weather soil, a rich source of all types of microbes, turns to dust and increases the airborne microbial population... 

Significant and active microbial populations are usually found in the subsurface soil and ground-water. However, if there is a lack of required microorganisms, then bacteria can be injected in situ. An optimum food/microorganisms (F/M) ratio should be maintained for effective removal of organic contaminants. 

Bioinfiltration is limited by the ability of soil microorganisms to degrade the contaminants of concern, since bacteria cannot metabolize or co-metabolize contaminants at toxic concentrations. Indigenous microbial populations require sufficient time to adapt to contaminants. 

Unfortunately there are only limited data available on soil microbial populations that can utilize phenolic acids as a carbon source. The CFU/g soil ranged from 104 to 1010 for bacteria in phenolic acid enriched air-dried soil and not enriched field soils (Table 3.1). However, these numbers of active, quiescent, and/or dormant individuals represent only a small fraction of the bacteria in these soils, since <1% of the viable bacteria in soils can be cultured.43 The assumption is that the CFU based on cultures are representative or consistently related to the... 

That microorganisms can reduce the observed phytotoxic effects of phenolic acids has been observed by a number of researchers.3,7 8 33 37 38 39 41,45 I am, however, not aware of any study that has attempted to quantify how changes in bulk-soil bacteria might influence the phytotoxicity of phenolic acids. I am aware of only one study that has attempted to quantify how changes in rhizosphere microbial populations may influence the phytotoxicity of phenolic acids. Blum et al.9 observed that a 500% increase of phenolic acid utilizing bacteria in the rhizosphere of cucumber seedlings growing in Cecil A-horizon soil enriched with an equimolar mixture of 0.6 pmol/g p-coumaric acid, ferulic acid, p-hydroxybenzoic acid, and... 

Smith, Z., McCaig, A., Stephen, J., Embley, T., and Prosser, J. I. (2001). Species diversity of uncultured and cultured populations of soil and marine ammonia oxidizing bacteria. Microbial Ecology 42, 228-237. 

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