Microbial, biomass

M. Moo-Young and K. F. Gregory, eds.. Microbial biomass Proteins, Elsevier AppHed Science PubHshers, Ltd., London, 1986. 

One of the most promising substrates for future production of microbial biomass is the ceUulose contained in agricultural residues such as wood pulp, sawdust, feed-lot waste, com stover, rice huUs, nut sheUs, and bagasse, aU of which contain ceUulose as the principal carbon source. CeUulose contents range from 90% in cotton to 15—20% in dicotyledon leaves. Wood residues and grasses contain mixtures of ceUulose, hemiceUulose, and lignin. The major... 

In any quantitative assessment of growth and/or product formation, it is essential to link formation of microbial biomass and products with the utilisation of substrate and nutrients. In the case of microbial biomass production, the total amount of cell mass yield formed is often proportional to the mass of substrate utilised. Mathematically this is coefficient expressed as the corresponding ratio, or yield coefficient ... 

The rate of product formation, rfi, depends upon the state of the cell population, environmental condition, temperature, pH, media composition and morphology with cell age distribution of the microorganism.2 3 A similar balance can be formulated for microbial biomass and cell concentration. The exponential phase of the microbial growth in a batch culture is defined by ... 

It is sometimes claimed that mucilage and similar gels may help to maintain hydraulic conductivity between root and. soil (52). However, the hydraulic conductivity of soils is often substantially decreased when soils are irrigated with waste water. Apart from the inducement of sodicity, which is real in many cases, the decreases in hydraulic conductivity are attributed largely to the production of microbial biomass, particularly extracellular polysaccharides (e.g.. Ref. 53). These extracellular polysaccharides form gels that may store large quantities of water and allow water and ions to diffu.se through them at rates not much less than those of free water, but they could be expected to restrict mass flow of water and thus nutrients, to roots (54). 

H. Bolton, L. F. Elliott, R, I, Papendick, and D, F. Bezdicek, Soil microbial biomass and selected soil enzyme activities effect of fertilisation and cropping practices. Soil Biology and Biochemistry 17 291 (1985),... 

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... 

Combining ammonium immobilization rates with estimates of C inputs and C maintenance requirement (proportional to the active microbial biomass), whose difference gave C available for microbial growth from the same experimental system (111,128), it allowed the building up of a conceptual model for C and N... 

Protocols for rhizosphere sampling need to be developed. Upon quantifying processes at the rhizosphere level, we may find whether large or small rhizosphere volumes or high or low rates of exudation are plant-specific and how they will benefit plants. This is not clear as yet and is an area for future research. In addition, reliable methods that enable us to distinguish between dormant and active soil microbial biomass could represent the crucial step in order to mechanistically understand C and N flows among plants, soil, and microbes in the rhizosphere. 

E. A. S. Rattray, E. Paterson, and K. Killham, Characterisation of the dynamics of C-partitioning within Loliiim perenne and to the rhizosphere microbial biomass using C pul.se chase. Biol. Fertil. Soils /9 280 (1995). 

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). 

H.-O. Nohrstedt, K. Arnebrant, E. Baiith, and B. Soderstrom, Changes in carbon content, re.spiration rate, ATP content, and microbial biomass in nitrogen-fertilized pine forest soils in Sweden. Can. J. For. Res. 79 323 (1989). 

P. C. Brookes, L. Landman, and D. S. Jenkin.son, Chloroform fumigation and the release of soil nitrogen a rapid extraction method to measure microbial biomass nitrogen in soil. Soil Biol. Biochem. 17331 (1985). 

L. Badalucco, F. De Cesare, S. Grego, L. Landi, and P. Nannipieri, Do soil physical properties affect the chloroform efficiency in lysing microbial biomass Soil Biol. Biochem. 29 1135 (1997). 

Numerical techniques are iterative and require considerable computer processing power. With modern desktop computers, this is usually not an issue and solutions of root uptake over days or weeks typically take a few seconds to generate. However, for some strongly nonlinear problems, such as the development of rhizosphere microbial populations (Sect. Ill), where the increase in microbial biomass may be exponential over time, processing time may become important with solutions requiring >60 min to calculate on a modern PC. 

Therefore if the carbon substrate is present at sufficiently high concentration anywhere in the rhizosphere (i.e., p p, ax), the microbial biomass will increase exponentially. Most models have considered the microbes to be immobile and so Eq. (33) can be solved independently for each position in the rhizosphere provided the substrate concentration is known. This, in turn, is simulated by treating substrate-carbon as the diffusing solute in Eq. (32). The substrate consumption by microorganisms is considered as a sink term in the diffusion equation, Eq. (8). 

Figure S The iimula(ed distribution of (u) soluble carbon and (b) microbial biomass in the rhizosphere of maize over a period of 10 days. The Jf axis represents distance (cm) from die rout surface and the Y axis represents time (h). A unifonn exudation rate (S3) is compared to the situation where the. siime amount of exudate is released in the first 24 h (S4). Note that the Z axes have different scales although both represent pg C cm (From Ref. 48.)...

H. Van der Werf and W. Verstraete, Estimation of active soil microbial biomass by mathematical analysis of respiration curves development and verification of the model. Soil Biol. Biochem. 19 252 (1987). 

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