Soil organic matter composition and microbial activity in urban soils

In an urban environment soil organic matter (SOM) has manifold functions and is of considerable ecological significance. In six top layers of soils of different ages in the city of Kiel at the Baltic Sea, Northwest Germany, the SOM composition was investigated by means of wet chemistry and CPMAS 13C-NMR spectroscopy and compared with data of natural soils and microbial eco-physiological parameters derived from basal respiration (Rmic), microbial biomass (Cmic) and total organic carbon (TOC). In comparison with natural soils, all urban soils were characterized by a very low level of the recalcitrant lipid fraction and the low molecular fulvic acid fraction. Cmic was-similar to those of their natural counterparts. The mean CmicTOC and the metabolic quotient (RmicCmic = qCO2) were higher, because of the young age of the soils and an early succession step, or due to environmental stress such as methane evolution. The logarithmic time dependant decline of CmicTOC was well correlated with the decrease of the available litter compounds in the SOM (proteins and polysaccharides). In the young soils ‘free’ litter compounds dominate in the SOM, whereas in the older soils 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 soil ecology in the urban environment.