Microbial Communities and Biomass

FIGURE 5.43 Conceptual model showing development of microbial community during cellulose decomposition in waterlogged soils (Adapted from Saito et al., 1990). 

Indices based on microbial activity, microbial biomass, SIR, and organic carbon have been proposed to provide an operationally defined means for describing the response of soil microbial populations to substrate quality and environmental conditions (see Chapter 15 for details). The ratio of MBC to soil organic carbon has been related to the soil organic carbon availability and 

FIGURE 5.44 Relationship between the aerobic respiration in soils and microbial biomass carbon (DeBnsk and Reddy, 1998). 

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The surface of the biofilm consists of a highly convoluted, tufted mat of microbial biomass. Diatoms were a common constituent of this microbial community, and their silaceous skeletons provide new surfaces for colonization. Most of the bacterial colonies consisted of a mixture of species and were of an open cylindrical shape, affording maximum aeration and nutrient exposure. 

Phospholipid fatty acid analysis (PLFA) is based on the determination of signature lipid biomarkers from the cell membranes and walls of microorganisms. Phospholipids are an essential part of intact cell membranes, and information from the lipid analysis provides quantitative insight into three important attributes of microbial communities viable biomass, community structure, and nutritional status. Phospholipid fatty acid prohles have been used to show the response of the microbial community to phosphorus availability (Keinanen et ah, 2002). Signature lipid biomarker analysis may not detect every species of microorganism in an environmental sample accurately, because many species have similar PLFA patterns. 

A. Tunlid and D. C. White, Biochemical analysis of biomass, community structure, nutritional status and metabolic activity of microbial communities in soil. Soil Biochemistry, vol 7 (G. Stotzky and J. M. Bollag, eds.) Marcel Dekker, New York, 1992, p. 229. 

S.L. Trabue, T.M. Crowe, and J.H. Massey, Changes in soil biomass and microbial community structure as affected by storage temperature and duration effect on the degradation of metsul-furon methyl in Pesticide Environmental Eate Bridging the Gap Between Laboratory and Eield Studies , ed. W. Phelps, K. Winton, and W.R. Effland, ACS Symposium Series 813, American Chemical Society, Washington, DC (2002). 

Historically, measurement of the microbial biomass has been a tedious, time-consuming occupation involving staining and direct counting or use of culture media and enumeration of individual microbial communities. However, in the last 20 years, a suite of methods have been developed for more rapid assessment of the microbial biomass. These include the substrate-induced respiration method (Anderson and Domsch 1978), the chloroform fumigation-incubation method (Jenkinson and... 

The qCC>2 is often used as an indicator of whether the microbial biomass is under stress. In general, factors that decrease the size of the microbial biomass tend to increase qC02. That is, factors that cause stress to the microbial community tend to reduce its size. Other factors could also contribute to an increased qC02. For example, bacterial communities are less efficient at converting substrate C into cellular C than fungi (Sakamoto and Oba 1994) so a change in the composition of microbial biomass can alter qC02 values. 

Certainly, calculation of the metabolic quotient can reveal trends very different from those of basal respiration. As shown in Fig. 1, for the 7 land uses, trends in basal respiration were broadly similar to those for microbial biomass C and organic C. However, when the metabolic quotient was calculated, trends with land use were very different. Values were greater under sugarcane, maize and to a lesser extent annual ryegrass, than the other treatments. This suggests that the microbial community under these arable land uses is under more stress and/or has a different composition to that under the others. The most likely microbial stress under these land uses is likely to be a shortage of available substrate C. 

Bohme L, Langer U, Bohme F (2005) Microbial biomass, enzyme activities and microbial community structure in two European long-term field experiments. AgrEcosyst Environ 109 141-152... 

Akmal M, Xu JM, Li ZJ, Wang HZ, Yao HY (2005a) Effects of lead and cadmium nitrate on biomass and substrate utilization pattern of soil microbial communities. Chemosphere 60 508-514... 

Frostegard A, Tunlid A, Baath E (1993) Phospholipids fatty acid composition, biomass, and activity of microbial communities from two soil types experimentally exposed to different heavy metals. Appl Environ Microbiol 59 3605-3617... 

Torsvic V, Goksoyr J, Daae FL, Sorheim R, Michalsen J, Salte K (1994) Use of DNA analysis to determine the diversity of microbial communities. In Ritz K, Dighton J, Giller KE (eds) Beyond the biomass compositional and functional analysis of soil microbial communities. John Wiley, Chichester, pp 39-48... 

Oline DK, Grant MC (2002) Scaling patterns of biomass and soil properties an empirical analysis. Landsc Ecol 17 13-26 Perez-de-Mora A, Burgos P, Madejon E, Cabrera F, Jaeckel P, Schloter M (2006) Microbial community structure and function in a soil contaminated by heavy metals effects of plant growth and different amendments. Soil Biol Biochem 38 327-341... 

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