The result may reflect differences in
the proportions of glucose-metabolizing microbes in these
soils. The methodology of substrate-induced respiration
(SIR) measurement assumes that the proportion of microorganisms
able to break down glucose is the same in each
soil (Anderson and Domsch 1978), but that may not be true
of every soil type. Anderson and Joergensen (1997) showed
that the extremely low pH and high organic matter content
of many forest soils may confound SIR estimates of
microbial biomass. The use of glucose to measure soil
respiration accurately may be problematic, but to measure
the soil microbial response shortly after contamination it is
necessary to use easily degradable carbon compounds.
Otherwise, the decay of dead microbial cells may measurably
increase the soil respiration rate, as Leita et al.
(1995)