References

Microbial Energetics in Soils 135
Fig. 6.Illustration of varying ratios between microbial respiration rate, Cmic and Corg content.
(After Dilly et al. 2001)
of the microbial biomass and a non-modified respiration rate are supported
by the same amount of organic matter (I, II). The increasing respiration
rate leads to the increasing quotient indicating enhanced C-use inefficiency
(III). This is unfavourable from an energetic perspective for soil microbial
communities as C for growth is lost. When the respiration rate, Cmic and
Corg content decrease proportionally, the qCO2/Corg ratio increases (IV).
Therefore, a scarce substrate level determines the efficiency value and,
thus, limited substrate will be evaluated. To summarise, the qCO2/Corg ratio
considers the following interrelations: (1) higher respiration leads generally
to increased inefficiency, (2) higher supported biomass enhances the
efficiency, (3) more available substrate can support more organisms or
biomass and enables higher activity (respiration), and (4) low quantity
and quality of substrates are considered in particular. Since variations in
microbial characteristics were frequently explained by changes in the Corg
content, the Cmic/Corg and qCO2/Corg ratios are structurally important indicators
of the interdependence between microbial communities and organic
matter and the energetic eco-physiological status as referring to different
C levels. Although factors such as substrate quality, the water and oxygen
supply and temperature in the respective biotope were not explicably
taken into consideration, the three ratios should lead to structural and
system-theoretical conclusions concerning the interaction between microbial
communities and organic matter in soils under different management
and land use (Dilly et al. 2001).