Hexosamines in the organic layer of two beech forest soils: effects of mesofauna exclusion

Summary

In December 1988, litter bags (mesh size: 45 and 1000 μm) were exposed in the organic layer of unlimed and limed moder soil under beech forest in the Solling area of Germany. Bags were retrieved on three sampling dates (May, September, and November 1989) and amounts (g m^-2) of glucosamine and galactosamine were determined. Horizon-specific differences generally explained by far the largest part of the treatment variance. In the substrate sampled in December 1988 from the unlimed area glucosamine increased by a factor of 11.8 from the L 1 layer to the H layer and galactosamine by a factor of 15.9. With the exception of the F2 layer, the hexosamine amounts found in the limed substrate sampled in December 1988 were higher in all horizons than in the corresponding horizons sampled from the unlimed area. Exclusion of mesofauna from the 45-μm litter bags generally reduced the level of amino sugars at both sites. The difference between the two mesh sizes was most pronounced in the lowermost horizons (F2 and H) and quite small in the upper horizons. The exclusion of mesofauna significantly increased the glucosamine: galactosamine ratio in the two L layers of the unlimed soil on all sampling dates. Seasonal fluctuations suggested that the actual amino sugar content of the organic layer was essentially the function of two components, the first reflecting long-term accumulation of microbial metabo-lites, and the second reflecting short term fluctuations in the microbial colonization of various C sources together with spatial and temporal differences in the ability of the microflora to produce and to decompose hexosamines. The results of this study show that the mesofauna in the beech forest soils investigated significantly affected both the amino sugar components measured, and thus stimulated the accumulation of one of the most important N pools in forest soils.