Biomass fumigation

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). 

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... 

Microbial biomass carbon Chloroform fumigation incubation Indicates soil microbial population various methodologies controls nutrient cycling and biological transformation necessary for soil aggregation dependent upon organic inputs Rice et al. (1996)... 

Microbial biomass P Chloroform fumigation extraction Indicate biologically active fraction of soil phosphorous control P cycle dependent upon organic amendments Brookes et al. (1982)... 

Methyl bromide is used as a fumigant for soils (the agricultural use shown in Table 12.7) and shipments of fruits and vegetables as well as for buildings for termite control (shown as structural purposes in Table 12.7). Large amounts are released during biomass burning (e.g., see Mano and Andreae, 1994 Cicerone, 1994)... 

Kassim, G., Martin J. R, and Haider, K. (1981). Incorporation of a wide variety of organic substrate carbons into soil biomass as estimated by the fumigation procedure. Soil Sci. Soc. Am. J. 45,1106-1112. 

Vance, Brookes, and Jenkinson (1987) first showed a close linear relationship between biomass C measured by the FI method and Ec, where Ec= [(organic C extracted by 0.5 molar (M) potassium sulfate (K2S04), soil fumigated for twenty-four hours) minus (organic C extracted from a similar, nonfumigated soil)]. They proposed that biomass C can be estimated from the relationship, Biomass C = 2.64 Ec. 

Chloroform fumigation also increases the amount of total N extractable with 0.5 M K2S04. Brookes et al. (1985) showed that this extra N also comes from the microbial biomass and proposed that biomass N could be estimated from the relationship, Biomass N = 2.22 EN, where EN is analogous to Ec. 

Hydrolytic enzymes remain active during CHC13 fumigation (Brookes 1982). Amato and Ladd (1988) showed that the amounts of ninhydrin-reactive compounds (i.e., ammonium, amino acids, peptides, and proteins) released from the biomass during fumigation and extracted by 2 M potassium chloride (KC1) are closely correlated to the initial biomass C concentrations. 

Biomass P (BP) is calculated from BP = (P extracted from fumigated soil minus P extracted from nonfumigated soil) x (l/kp) x (100/R), where kp is the fraction of Bp released by CHC13 (0.40) and extracted by 0.5 M NaHC03 and R is the percentage recovery of the spike of added inorganic P. The results are expressed as pg BP g-1 soil. 

The weight of soil used in the measurement depends on the initial soil microbial biomass concentration and the flask volume. Normally, 20-40 g moist soil is suitable for this measurement. Lin and Brookes (1999a) showed that SIR can give reliable estimates of microbial biomass in unamended soils, soils that contain actively decomposing plant residues, or soils recently treated with pesticides or fumigants. The final results are usually expressed as the SIR rate (tl C02 evolved g soil h Biomass carbon (Bc) is estimated by Bc (gig C g l soil) = 15 SIR (Lin and Brookes 1999a). 

Amato, M. and Ladd, J. N. (1988). Assay for microbial biomass based on ninhy-drin-reactive nitrogen in extracts of fumigated soils. Soil Biol. Biochem. 20, 107-114. 

Brookes, P. C., Landman, A., Pruden, G., and Jenkinson, D. S. (1985). Chloroform fumigation and the release of soil nitrogen A rapid direct extraction method to measure microbial biomass nitrogen in soil. Soil Biol. Biochem. 17, 837-842. Brookes, P. C., Powlson, D. S., and Jenkinson, D. S. (1982). Measurement of microbial biomass phosphorus in soil. Soil Biol. Biochem. 14, 319-321. 

Inubushi, K., Brookes, P. C and Jenkinson, D. S. (1991). Soil microbial biomass C, N and ninhydrin-N in aerobic and anaerobic soils measured by the fumigation-extraction method. Soil Biol. Biochem. 23,737-741. 

Mueller, T Joergensen, R. G., and Meyer, B. (1992). Estimation of soil microbial biomass C in the presence of living roots by fumigation-extraction. Soil Biol. Biochem. 24,179-181. 

ISO 14240-2 1997 Soil quality - Determination of soil microbial biomass -Part 2 Fumigation-extraction method. 

The size of Che microbial populations able to rapidly degrade carbofuran in soils enhanced for its degradation were enumerated by means of substrate addition and fumigation. Use of these techniques followed unsuccessful attempts to enumerate the population using plate or direct counts in the enhanced soils. Overall biomass size declined following application of carbofuran. No biomass suppression was observed in the non-enhanced soils and implies this suppression may be related to the formation of metabolites such as carbofuran-phenol or methylamine. In the enhanced soils, 6% of applied pesticide was initially incorporated into biomass carbon. This contrasts with 0.87% incorporation in the non-enhanced soils. After 15 days there was complete loss of Che pesticide at this time the biomass contained 2% of the applied material. 

The substrate addition method for biomass estimation relies on the fact that the biomass response to the introduction of the pesticide is reflected in the response to the glucose. Fumigation relies on the conversion of the specifically labeled biomass to C-C02- From both estimations it is clear that the size of microbial biomass that can use the carbon in the carbofuran side-chain is small. Karns et al. (11) has shown that carbofuran may serve as nitrogen source for some organisms. Our estimates would overlook this N utilization. It is likely that organisms that utilize methylamine, the primary degradation product, for nitrogen would overlook this source of carbon. Data on bacterial use of methylamine is, however, limited. 

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