Anaerobic oxalate consumption by microorganisms in forest soils.

The microbial consumption of oxalate was examined under anaerobic conditions in soil suspensions at 15-20 degrees C. With soil (horizon Ah, pH 6.4) from a beech forest, microbial consumption of added oxalate (15mM) began after 10days, and oxalate was totally consumed by day 20. The presence of supplemental electron donors (acetate, glucose, vanillate, or hydrogen) or electron acceptors (nitrate or sulfate) did not significantly influence anaerobic oxalate consumption, whereas supplementation of soil suspensions with CO(2)/bicarbonate totally repressed oxalate consumption. Thus, CO(2)-, nitrate- or sulfate-respiring bacteria were apparently not active in the anaerobic consumption of oxalate in these soil suspensions. With soil (horizon Bt, pH 7) from a beech forest, oxalate consumption began after an approximate lag of 14days, and oxalate was totally consumed by day 41. With both soils, acetate was the major aliphatic organic acid detected during oxalate consumption. Near pH-neutral soils from two additional forest field sites were also competent in anaerobic oxalate consumption. In contrast, anaerobic oxalate consumption was negligible in suspensions prepared with acidic soils (<pH 4.2) collected from three different forest field sites. These results suggest that forest soils and their resident microbial populations have different capacities relative to anaerobic oxalate consumption.