Origin of the enriched labile fraction (ELF) in Russian Chernozems with different site history

It was assumed that protected soil organic matter (SOM) inside small macroa ggregates is indicated by the enriched labile fraction (ELF) (2.07-2.22 g c m(-3) of aggregated fine silt). The ELF should be of fungal origin and sens itively reflect management effects on SOM. To test these hypotheses, we hav e isolated ELF from mollic epipedons (0-10 cm) of Chernozems under native s teppe, meadow, forest, and long-term arable land. The ELF was characterized by C, N, amino-sugar and C-13-CP/MAS-NMR measurements. The results showed that the glucosamine to-muramic acid ratio was higher in ELF than in other aggregate-density fractions. This indicated that microbial residues in the ELF, stronger than in other fractions, are of fungal origin. The remaining SOM composition as identified by C-13-CP/MAS-NMR spectroscopy was not diffe rent from that of the other density fractions. The ELF was therefore enrich ed in fungal debris but it did not solely consist of microbial N. Neverthel ess, ELF seemed to reflect land-use effects on SOM. The C and N loss from E LF due to arable land use or afforestation resulted in a relative preservat ion of its bacterial-derived muramic acid relative to glucosamine, however, due to the lack of independent replicates such effects could not be statis tically evaluated. (C) 2001 Elsevier Science B.V. All rights reserved.