Long-term effects of liming on microbial biomass and activity and soil organic matter quality (13C CPMAS NMR) in organic horizons of Norway spruce forests in Southern Germany

Long-term effects of liming on microbial biomass and activity and soil organic matter (SOM) were investigated in samples from organic horizons (Of/Oh) in spruce forests at Adenau, Hoglwald, Idar-Oberstein, and Schluchsee (Southern Germany) where plots have been manually treated 7 to 13 years ago with dolomitic limestone. At all sites, pH values were markedly increased after liming. The contents of C and N in the organic horizons of the limed plots appeared to be lower with the greatest decrease at Hoglwald (Dystric Luvisol) where liming has affected the soil properties for the longest time of all sites. Catalase activity was promoted after liming at Adenau (Cambic Podzol). This was also the case for the Dystric Luvisol where liming resulted also in higher basal respiration. Biomass-C was higher in samples from the limed plot at Idar-Oberstein (Dystric Cambisol). The C-13 CPMAS NMR spectra of organic horizons from the control plots indicate no differences in the gross carbon composition of SOM. Furthermore, spectra from the limed Cambic Podzol, Dystric Cambisol, and Haplic Podzol (Schluchsee) were remarkably similar. However, for the Dystric Luvisol. the lime-induced promotion of microbial activity resulted in lower O-alkyl-C intensity. The observed patterns of microbial biomass and activity were site-dependent rather than a result of liming. Obviously liming had only small long-term effects on the humus quality in the organic horizons, as far as detectable by CPMAS NMR spectroscopy. More sensitive techniques like pyrolysis-GC/MS should be applied to analyze differences in C composition.