Microbial respiration
Microbial respiration is essentially breathing by microbes, and is considered the final step in decomposition. Microbes use carbon-rich molecules (organic matter) as a source of energy and nutrients. Breaking down these molecules releases carbon dioxide (CO2). The amount of nutrients and carbon packed into organic matter (this can be leaves, residues, manures, organic matter in the soil, etc.) usually occur at different proportions (ratios C:N, C:P) than the microbes need for growth. This can influence the efficiency with which organic matter is broken-down and determines how much carbon and nitrogen is released during the process or whether extra nutrients, such as nitrogen or phosphorus are needed from the surrounding soil.
Microbial respiration directly contributes to decomposition in the Carbon Sequestration and Climate Regulation function, as it concerns the release of the greenhouse gas CO2. Because the recycling of carbon and nitrogen are tightly coupled, mineralisation in the Nutrient Cycling function is its counterpart. Respiration is a biologically active process; this means that release of carbon (respiration) by microbes coincides with the uptake of carbon and nutrients (microbial assimilation) and thus relates to carbon and nutrient flows in the food web assimilation process for both the and Climate Regulation and Nutrient Cycling functions.
Common methods to measure microbial respiration rely on measuring the change in CO2 concentration in the airspace above the soil or other type of samples in a closed space over a period of time. This evolution of CO2 can be measured by chemical trapping[1],[2] or with gas analyzers[3]. Microbial respiration can also be measured as part of the broader catabolic profiling with MicroRespTM [4].
[1] Liu W et al. 2009. Predominant role of water in regulating soil and microbial respiration and their responses to climate change in a semiarid grassland. Global Change Biology 15: 184–195.
[2] Witkamp M. 1966. Decomposition of leaf litter in relation to environment, microflora and microbial respiration. Ecology 47: 194–201.
[3] Robertson GP et al. 1999. Soil carbon and nitrogen availability: Nitrogen mineralization, nitrification, and soil respiration potentials. In Standard soil methods for long-term ecological research: 258–271 (Oxford University Press).
[4] Campbell CD et al. 2003. A rapid microtiter plate method to measure carbon dioxide evolved from carbon substrate amendments so as to determine the physiological profiles of soil microbial communities by using whole soil. Applied and Environmental Microbiology 69: 3593–3599.