Substrate-induced respiration
The substrate-induced respiration (SIR, English: substrate-induced respiration) is an indirect method for determining the microbial biomass in soils . It was described in 1978 by JPE Anderson and KH Domsch (Institute for Soil Biology at the Research Institute for Agriculture, Braunschweig ).
principle
The SIR method is based on the fact that microorganisms react immediately with the addition of a readily available carbon source (e.g. glucose ) with increased respiration - i.e. substrate-induced respiration . The amount of carbon dioxide released in the process can be determined by gas chromatography or infrared gas analysis and related to the microbial activity or biomass using an empirical formula.
Anderson & Domsch (1978) found that 1 ml of glucose-induced released CO 2 per dry substance in one hour at 22 ° C corresponds to 40.04 mg of microbial biomass carbon. The biomass ( dry mass ) of the microorganisms is then obtained from the proportion of carbon in the total biomass - generally around 45%.
Formula for calculating the microbial biomass:
evaluation
The advantage of the SIR method lies in its good reproducibility and the relatively low expenditure of work and time. Strictly speaking, however, the lowest glucose concentration with the maximum respiratory response must always be determined first. If too little glucose is added, the biomass is underestimated; if too much is added, the microorganisms grow, which falsifies the result. This preparatory work naturally increases the effort. In practice, however, this can often be dispensed with because only comparative statements are to be made (for example, is the microbial biomass greater at one location than at another?). In addition, specific inhibitors can be used to differentiate between different groups of microorganisms or between microorganisms and fungi . Microorganisms in the active and vegetative stage can not be distinguished with this method .
literature
- Anderson, JPE and Domsch, KH (1978): A physiological method for the quantitative measurement of microbial biomass in soils. Soil Biology and Biochemistry 10, 215-221