Effect of Flooding on Microbial Activities in Organic Soils

Changes in the microbial activities during and after flooding of Pahokee muck were examined and compared to variations in soil samples incubated under anaerobic conditions in the laboratory. Overall aerobic metabolism, as measured by 14C-labeled succinate oxidation, in the field decreased approximately 65 percent during the first 10 days of flooding and remained at that level until the field was drained. This compared to an 88 percent decrease in soil incubated anaerobically in the laboratory.Aromatic ring catabolism (salicylate oxidation) was most sensitive to flooded conditions. A 90 percent decrease was detected in the oxidation rate for salicylate during flooding. Catabolic rates of amino acids, glucose, and acetate decreased to a lesser extent. The aerobic and facultative bacterial populations increased approximately threefold during the first 10 days of flooding. These populations then decreased until the field was drained when, again, a threefold increase in the numbers occured. Dehydrogenase activity declined during the first five days of flooding; then it increased continually until the field was drained. At that point, the enzymic activity decreased. These data indicate the decling importance of aerobic carbon metabolism during flooding and suggest an increase in the facultative and anaerobic populations. The complex aromatic ring structures became more resistant to microbial attack during flooding, andt he importance of amino acids and carbohydrates in the carbon metabolism by the micrbial community increased.