Acetogenic capacities and the anaerobic turnover of carbon in a kansas prairie soil.

To assess the anaerobic capacities of a temperate grassland soil, a Kansas prairie soil was incubated anaerobically as either soil-water (1:2) suspensions or as soil microcosms at 78% soil water-holding capacity. Prairie soil formed acetate and CO(inf2) as the two main initial carbonaceous products from the anaerobic turnover of endogenous organic matter. Metabolic capacities of soil suspensions and microcosms were similar. Rates of acetate formation from endogenous organic matter in soil-water suspensions incubated at 40, 30, and 15(deg)C approximated 3.3, 2.4, and 1.1 (mu)g of acetate per g (dry weight) of soil per h, respectively. Supplemental H(inf2) and CO(inf2) were subject to consumption with the apparent concomitant synthesis of acetate in both soil suspensions and soil microcosms. In soil microcosms, rates of H(inf2)-dependent acetogenesis at 30 and 55(deg)C were nearly equivalent. The uptake of supplemental H(inf2) was not coupled to methanogenesis under any condition examined. These anaerobic activities were relatively stable when soils were subjected to either aerobic drying or alternating periods of O(inf2) enrichment. On the basis of the formation of nitrogen (N(inf2)), denitrification was engaged during anaerobic incubation periods; nitrous oxide (N(inf2)O) was also formed under certain conditions. Although extended incubation of soil induced the delayed methanogenic turnover of acetate, acetate was subject to immediate turnover under either O(inf2)- or nitrate-enriched conditions. These studies support the following concepts: (i) obligately anaerobic bacteria such as acetogenic bacteria are stable to periods of aerobiosis and are active in the anaerobic microsites of oxic soils, and (ii) acetate synthesized in anaerobic microsites of oxic terrestrial soils constitutes a trophic link to both aerobic and anaerobic microbial communities.