CARBOHYDRATE DECOMPOSITION IN BEECH LITTER AS INFLUENCED BY ALUMINUM,IRON AND MANGANESE OXIDES

Although carbohydrates are one of the most degradable groups of soil o rganic matter compounds, they can accumulate in soil horizons containi ng strongly humified organic matter. It is therefore assumed that stab ilization reactions exist, which may be related to the presence of par ticular mineral compounds in soils. An incubation experiment was made to investigate the influence of selected oxides (ferrihydrite, alumini um hydroxide, birnessite) on the decomposition of polysaccharides in b eech litter. pH changes and the-dynamics of total organic carbon, cell ulosic and non-cellulosic polysaccharides, and potential cellulase act ivity were recorded. Carbon loss during incubation was promoted by 10% in the presence of birnessite, which acts as an oxidizing agent. Poly saccharide decomposition was hardly affected by birnessite. On the oth er hand, ferrihydrite and aluminium hydroxide reduced the decompositio n of bulk organic matter by 12 and 65%, respectively. These mineral ph ases resulted in a reduction of carbohydrate decomposition by 15 and 5 0%, respectively. In the presence of aluminium hydroxide, there was no significant cellulose decomposition after 90 d. Nevertheless, through out the experiment, potential cellulase activity was higher in this tr eatment than in the presence of birnessite. Therefore we assume that o rganic matter stabilization is caused by toxic effects, or by adsorpti on to the oxides or hydroxides, especially to aluminium hydroxide, or by both. This process tends tb lower the microbial availability of org anic matter and therefore to inhibit the decomposition. (C) 1997 Elsev ier Science Ltd.