SOIL ORGANIC-MATTER COMPOSITION AND MICROBIAL ACTIVITY IN URBAN SOILS

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.