ACETOGENIC CAPACITIES AND THE ANAEROBIC TURNOVER OF CARBON IN A KANSAS PRAIRIE SOIL

To assess the anaerobic capacities of a temperate grassland soil, a Ka nsas prairie soil was incubated anaerobically as either soil-water (1: 2) suspensions or as soil microcosms at 78% soil water-holding capacit y. Prairie soil formed acetate and CO2 as the two main initial carbona ceous products from the anaerobic turnover of endogenous organic matte r, Metabolic capacities of soil suspensions and microcosms were simila r. Rates of acetate formation from endogenous organic matter in soil-w ater suspensions incubated at 40, 30, and 15 degrees C approximated 3. 3, 2.4, and 1.1 mu g of acetate per g (dry weight) of soil per h, resp ectively, Supplemental H-2 and CO2 were subject to consumption with th e apparent concomitant synthesis of acetate in both soil suspensions a nd soil microcosms. In soil microcosms, rates of H-2-dependent acetoge nesis at 30 and 55 degrees C were nearly equivalent, The uptake of sup plemental H-2 was not coupled to methanogenesis under any condition ex amined. These anaerobic activities were relatively stable when sails w ere subjected to either aerobic drying or alternating periods of O-2 e nrichment, On the basis of the formation of nitrogen (N-2), denitrific ation was engaged during anaerobic incubation periods; nitrous oxide ( N2O) was also formed under certain conditions. Although extended incub ation of soil induced the delayed methanogenic turnover of acetate, ac etate was subject to immediate turnover under either O-2- or nitrate-e nriched conditions, These studies support the following concepts: (i) obligately anaerobic bacteria such as acetogenic bacteria are stable t o periods of aerobiosis and are active in the anaerobic microsites of oxic soils, and (ii) acetate synthesized in anaerobic microsites of ox ic terrestrial soils constitutes a trophic link to both aerobic and an aerobic microbial communities.