EFFECTS OF ENVIRONMENTAL PARAMETERS ON THE FORMATION AND TURNOVER OF ACETATE BY FOREST SOILS

The capacity to form acetate from endogenous matter was a common prope rty of diverse forest soils when incubated under anaerobic conditions, At 15 to 20 degrees C, acetate synthesis occurred without appreciable delay when forest soils were incubated as buffered suspensions or in microcosms at various percentages of their maximum water holding capac ity. Rates for acetate formation with soil suspensions ranged from 35 to 220 mu g of acetate per g (dry weight) of soil per 24 h, and maxima l acetate concentrations obtained in soil suspensions were two- to thr eefold greater than those obtained with soil microcosms at the average water holding capacity of the soil, Cellobiose degradation in soil su spensions yielded H-2 as a transient product. Under anaerobic conditio ns, supplemental H-2 and CO2 were directed towards the acetogenic synt hesis of acetate, and enrichments yielded a syringate-H-2-consuming ac etogenic consortium. At in situ temperatures, acetate was a relatively stable anaerobic end product; however, extended incubation periods in duced acetoclastic methanogenesis and sulfate reduction, Higher mesoph ilic and thermophilic temperatures greatly enhanced the capacity of so ils to form methane, Although methanogenic and sulfate-reducing activi ties under in situ-relevant conditions were negligible, these findings nonetheless demonstrated the occurrence of methanogens and sulfate-re ducing bacteria in these aerated terrestrial soils, In contrast to the protracted stability of acetate under anaerobic conditions at 15 to 2 0 degrees C with unsupplemented soils, acetate formed by forest soils was rapidly consumed in the presence of oxygen and nitrate, and substr ate-product stoichiometries indicated that acetate turnover was couple d to oxygen-dependent respiration and denitrification. The collective results suggest that acetate formed under anaerobic conditions might c onstitute a trophic link between anaerobic and aerobic processes in fo rest soils.