In an urban environment soil organic matter (SOM) has manifold functio
ns and is of considerable ecological significance. In six top layers o
f soils of different ages in the city of Kiel at the Baltic Sea, North
west Germany, the SOM composition was investigated by means of wet che
mistry and CPMAS C-13-NMR spectroscopy and compared with data of natur
al soils and microbial eco-physiological parameters derived from basal
respiration (R(mic)), microbial biomass (C-mic) and total organic car
bon (TOC). In comparison with natural soils, all urban soils were char
acterized by a very low level of the recalcitrant lipid fraction and t
he low molecular fulvic acid fraction. C-mic was similar to those of t
heir natural counterparts. The mean C-mic/TOC and the metabolic quotie
nt (R(mic)/C-mic = qCO(2)) were higher, because of the young age of th
e soils and an early succession step, or due to environmental stress s
uch as methane evolution. The logarithmic time dependant decline of C-
mic/TOC was well correlated with the decrease of the available litter
compounds in the SOM (proteins and polysaccharides). In the young soil
s 'free' litter compounds dominate in the SOM, whereas in the older so
ils these SOM compartments were incorporated into the humic matrix by
probably reducing their availability to microorganisms. In summary in
the urbic soils humification has to be enhanced in order to improve so
il ecology in the urban environment.