Fate of microbial residues during litter decomposition as affected by minerals

Minerals may protect organic matter against microbial decay, either by dire ct chemical and physical interactions or by inhibitory effects on the soil microbial community. To clarify the effects of minerals on organic matter c ycling by microorganisms, we used amino sugars as tracers for C and N in de ad microbial cells after 0, 15, 29, 90, 239, and 498 days of incubation of beech leaf litter mixed with quartz sand, Fe oxide, Al hydroxide, or Mn oxi de. Beech leaf litter without addition of any mineral phases was used as th e control. The results show that amino sugar concentrations increased as li tter decomposition proceeded. Decreasing ratios of glucosamine to muramic, acid and of glucosamine to galactosamine indicated that bacterial products accumulated increasingly relative to fungal cells with increasing incubatio n time. As the presence of Mn oxide promoted losses of plant-derived C, the re was a more pronounced selective accumulation of the microbial-derived am ino sugar C than in the other treatments. Aluminium hydroxide and Fe oxide inhibited synthesis of bacterial amino sugars by a factor of two. This resu lted in lower amino sugar C proportions. compared with the other treatments . Consequently, the amino sugar C proportions were sensitive to both increa sing amino sugar synthesis and C mineralization rates. In contrast, the ami no sugar N proportions were not affected by any mineral additions. Thus, th e mere presence of minerals did not affect the cycling of N through the, am ino sugar pool, but minerals. altered the relative proportions of N sequest ered within residues of bacteria and fungi.