Field experiment is described in detail.
Briefly, the 12 12 m field was divided into four quadrants, for four
replications. PVC-tubes (diameter: 10 cm, height: 13 cm) were
installed 10 cm deep in the soil. 10 ml tracer-solution per column
were applied with a multipette (Eppendorf, Hamburg, Germany)
with concentrations of 13C-labeled sugars according to Table 1. A
7 cm long needle with lateral holes enabled homogeneous distribution
of the tracer solution within the column. The solution was
only injected in the upper 2/3 of the column to avoid leaching and
rainfall was blocked by a roof. In each of the quadrants and for both
sampling times, glucose and ribose were applied once as 1) nonlabeled
background, 2) uniformly 13C-labeled, and 3) as four and
two position-specific 13C-labeled isotopomeres of glucose and
ribose, respectively (see Table 1) with a random distribution within
the block.