HEXOSAMINES IN THE ORGANIC LAYER OF 2 BEECH FOREST SOILS - EFFECTS OFMESOFAUNA EXCLUSION

In December 1988, litter bags (mesh size: 45 and 1000 mum) were expose d in the organic layer of unlimed and limed moder soil under beech for est in the Solling area of Germany. Bags were retrieved on three sampl ing dates (May, September, and November 1989) and amounts (g m-2) of g lucosamine and galactosamine were determined. Horizon-specific differe nces generally explained by far the largest part of the treatment vari ance. In the substrate sampled in December 1988 from the unlimed area glucosamine increased by a factor of 11.8 from the L1 layer to the H l ayer 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 t he 45-mum litter bags generally reduced the level of amino sugars at b oth sites. The difference between the two mesh sizes was most pronounc ed in the lowermost horizons (F2 and H) and quite small in the upper h orizons. The exclusion of mesofauna significantly increased the glucos amine:galactosamine ratio in the two L layers of the unlimed soil on a ll sampling dates. Seasonal fluctuations suggested that the actual ami no sugar content of the organic layer was essentially the function of two components, the first reflecting long-term accumulation of microbi al metabolites, and the second reflecting short term fluctuations in t he microbial colonization of various C sources together with spatial a nd temporal differences in the ability of the microflora to produce an d to decompose hexosamines. The results of this study show that the me sofauna in the beech forest soils investigated significantly affected both the amino sugar components measured, and thus stimulated the accu mulation of one of the most important N pools in forest soils.