ACETATE CONCENTRATIONS AND OXIDATION IN SALT-MARSH SEDIMENTS

Acetate concentrations and rates of acetate oxidation and sulfate reduction were measured in Spartina alterniflora sediments in New Hampshire and Massachusetts. Pore water extracted from cores by squeezing or centrifugation contained >0.1 mM acetate and in some instances > 1.0 mM. Pore water sampled nondestructively contained much less acetate, often <0.01 mM. Acetate was associated with roots, and concentrations varied with changes in plant physiology. Acetate turnover was very low whether whole-core or slurry incubations were used. Radiotracers injected directly into soils yielded rates of sulfate reduction and acetate oxidation not significantly different from core incubation techniques. Regardless of incubation method, acetate oxidation did not account fora substantial percentage of sulfate reduction. These results differ markedly from data for unvegetated coastal sediments where acetate levels are low, oxidation rate constants are high, and acetate oxidation rates greatly exceed rates of sulfate reduction. The discrepancy between rates of acetate oxidation and sulfate reduction in these marsh soils may be due to the use of substrates other than acetate by sulfate reducers or to artifacts associated with measurements of organic use by rhizosphere bacteria.