References

Microbial Energetics in Soils 133
observed when the substrate was added in one dose as in the silver fir forest
soil with highest native biomass (Fig. 5).
Respiratory coefficient values of approximately 0.75 were frequently
recorded in the literature for incubation times of 5 h and up to 5 days
(summarised by Joergensen 1995). The values in Fig. 5, which were determined
after 7 days, ranged from 0.0 to 1.45 µgCmic µg −1 CO2 − C and thus
represent a broad spectrum of microbial responses to the nutrient addition
in agricultural and forest soils of different quality.
4.3
Soil Organic C, Microbial C and Biological Active C
and Interactions with N
In comparison to agricultural or peat topsoils that contain in the range of 10
to 500 mg organic C g −1 soil, the basal mineralisation rate varies on average
between 0.5 and 300 µg CO2-C g −1 soil h −1 under optimised conditions
with 40–70% water holding capacity (WHC) and 22 ◦ C.Topsoilsregularly
contain a microbial biomass from 50 to 5000 µg Cmic g −1 soil. Thus, the
microbial quotient can be modified from 0.5 and 10 mg Cmic g −1 Corg and
the metabolic quotient from 0.5 and 10 mg CO2-C g −1 Cmic h −1 (Fig. 4).
Interaction between stable and labile carbon and nitrogen pools can be
evaluated by looking at the soil C/N and Cmic/Nmic ratio and the biologically
active C and N and, furthermore, the qCO2 and qNmin (Dilly et al. 2003).
5
Holistic Approaches to Evaluate Energetic Strategies
of Soil Microbial Communities
Microorganisms dominate the biological component in most soils and
respond rapidly to changing environmental conditions. These organisms
are essential for many soil functions, but, in turn, their capabilities are
controlled by environmental constraints.
The contents of soil organic matter (SOM) and microbial biomass (Cmic),
both key factors of soil quality, are often closely correlated (Elliott 1997).
However, Anderson and Domsch (1989) showed that the ratio between microbial
biomass and organic matter content is adjusted to soil management
in agricultural ecosystems, being higher in crop rotation systems and after
application of organic fertiliser. Anderson and Gray (1991) observed
higher values of up to 4% briefly after organic fertilisation, dropping afterwards
to a site-specific and perhaps soil-quality characteristic level. In
litter, values up to 8% can be found (Dilly and Munch 1996). In addition,