Microbial biomass of soil

All cell culture-based methodologies are essentially limited when studying whole microbial populations, since the dominant proportion of microbial biomass of soil, rhizosphere and rhizoplane, and other environments cannot be cultured on standard laboratory media (114). To obtain information on the composition and activity of the nonculturable fraction and to aid the study of the culturable fraction, direct detection methods are needed. 

Absorption bands in the typical C—H stretching region at 3000-2870 cm-1 usually showing two maxima at 2925 and 2855 cm-1 related to CH2 and CH3 aliphatic groups. These bands are well defined in the spectra obtained from microbial biomass of soils and there can be assigned to cell wall and capsular polysaccharides (Filip, 1978) 27). But they are also common in spectra of other biological materials. 

The incorporation of several phenolic compounds into humified organic matter, and into the microbial biomass of soil, was studied by Kassim et all, They found that substantial proportions of the intact molecules of phenolic compounds, such as ferulic acid and catechol, were stabilised by incorporation into existing humus. Incorporation into the microbial biomass was greatest during the first two to four weeks of incubation, after which the amount declined with a corresponding increase in the proportion evolved as CO2. 

Information is contradictory about the contributions of root-derived C to the C pools available to the root zone and how this readily available C affects the subsequent associated microbial transformations of soil N (107). In a greenhouse experiment that involved growing maize plants and using C natural abundance and isotope "N techniques, 15% of the soil microbial biomass was derived from... 

Anderson JPE, Domsch KH (1978) A physiological method for the quantitative measurement of microbial biomass in soils. Soil Biol Biochem 10 215-221 Anderson TH, Domsch KH (1990) Application of eco-physiological quotients (qC02 and qD) on microbial biomasses from soils of different cropping histories. Soil Biol Biochem 22 251-255... 

Anderson TH, Domsch KH (1993) The metabolic quotient for C02 (qC02) as a specific activity parameter to assess the effects of environmental conditions, such as pH, on the microbial biomass of the soil. Soil Biol Biochem 25 393-395... 

Ocio JA, Brookes PC, Jenkinson DS (1991) Field incorporation of straw and its effects on soil microbial biomass and soil inorganic N. Soil Biol Biochem 23 171-176... 

Ajwa, H. A., C. J. Dell, and C. W. Rice. 1999. Changes in enzyme activities and microbial biomass of tallgrass prairie soil as related to burning and nitrogen fertilization. Soil Biology and Biochemistry 31 769-777. 

Mineralization of organic residues in soil is mainly carried out by an extremely diverse heterotrophic community referred to as the soil microbial biomass. The soil environment is a rather peculiar natural environment for the growth of microorganisms, in that they have had to adapt to quite extreme growth-limiting factors (a) discontinuous availability of substrates and water and (b) high variability of soil chemical properties (pH, temperature, oxygen supply) that can vary in the soil environment on both the micro and macro scales (Jenkinson and Ladd, 1981). 

Entry, J.A., P.K. Donnelly, and W.H. Emmingham (1995a). Atrazine and 2,4-D mineralization in relation to microbial biomass in soils of young-, second-, and old-growth riparian forests. Appl. Soil Ecol., 2 77-84. 

Microscopic counting is still the most direct method of estimating the amount of microbial biomass in soil but is technically difficult and completely unsuitable for routine use. Thin films are prepared from an agar-soil suspension, are mounted on microscope slides, and then are treated with an appropriate stain. Phenolic aniline blue is often used as it stains protein and is thus considered to give an estimate of the entire population. The numbers... 

Ocio, J. A. and Brookes, P. C. (1990a). An evaluation of methods for measuring the microbial biomass in soils following recent additions of wheat straw and the characterization of the biomass that develops. Soil Biol. Biochem. 22, 685-694. 

Gregorich E. G., Voroney R. P., and Kachanoski R. G. (1991) Turnover of carbon through the microbial biomass in soils with different textures. Soil Biol. Biochem. 23(8), 799-805. 

Figure H. Relationship between the phosphorus and carbon contained in microbial biomass of 14 soils (Brookes et al, 1984).

Several interrelated factors complicate the relationship between growth and degradation multispecies interactions, cometabolic degradation, and substrate utilization. If multispecies consortia are required for degradation, then the amount of pesticide incorporated into microbial biomass of a particular species may be even lower. Multispecies interactions have been investigated Lappin et al. (21) isolated a consortium of 5 bacteria that metabolized the herbicide mecoprop in culture after a lag period of 20 hr. The growth of the consortium was in contrast to the failure of individual species to grow on mecoprop. The extent of these kinds of interactions in soils is essentially unknown. 

Anderson, J.P.E. and Domsch, K.H. (1 980) Quantities of plant nutrients in the microbial biomass of selected soils. Soil Science 1 30, 211 -21 6. 

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