However, trends for lower recovery of glucose 13C-1
and 13C-4 and ribose 13C-1 in soil could be perceived on day 3.
These trends were significant on day 10: 1) glucose 13C-1 was
recovered significantly less in soil than glucose 13C-6 and 2) ribose
13C-1was incorporated significantly less than 13C-5. However, there
was no significant difference in tracer-C recovery in soil of the sugar
positions between day 3 and 10. All of the tracer-C that was stabilized
in soil at day 3 remained on day 10. In microbial biomass, we
observed equal recoveries of glucose 13C-1 and 13C-4, which were
lower than the equally high recoveries of glucose 13C-2 and 13C-6 on
day 3. There was also more than twice as much ribose 13C-5 than
13C-1 extracted in microbial biomass on day 10. In contrast to bulk
soil, in microbial biomass we saw a significant decrease of tracer C
recovery from glucose C-2, C-4 and C-6 and also ribose C-5 between
day 3 and 10. Additionally, not only did the overall tracer recovery
decrease, but also the pattern of incorporation of individual positions
changed.We observed an especially high decrease in tracer C
recovery from glucose C-2 (90%) and ribose C-5 (70%). As there
was no corresponding decrease in soil, these positions were
considered to be stabilized in the soil as microbial residues.
As absolute incorporation of tracer 13C into
P
-PLFA was much
lower than into the other two pools, the DI aids in the observation
of the sugar positions' incorporation pattern into
P
-PLFA (see
Supplementary, Figure 1). Interestingly, on day 3, the incorporation
pattern of glucose positions into
P
-PLFA was different to that of
microbial biomass: we found a preferential incorporation of
glucose 13C-2 and the highest discrimination against glucose 13C-4.
On day 10, the difference in the relative incorporation of individual
positions was no longer significant.