Regulators of heterotrophic microbial potentials in wetland soils

Potential rates of aerobic respiration, denitrification, sulfate reduction and methanogenesis were investigated in 10 different wetland soils with a wide range of biogeochemical characteristics, with the objective of determining relationships between process rates and soil properties. Electron acceptor amendments to methanogenic soils caused gradual (1–13 d) to immediate transitions in electron flow from methanogenesis to alternate electron acceptors. Rates of organic C mineralization ranged between 0.2 and 34 μmol C g−1 d−1 and averaged three times faster with O2 as compared to alternate electron acceptors. There was no significant difference between rates of organic C mineralization (CO2+CH4 production) under denitrifying, sulfate-reducing and methanogenic conditions, indicating that soil organic carbon availability was similar under the different anaerobic conditions. Rates of electron acceptor consumption ranged between 1 and 107 μmol g−1 d−1 for O2, 0.5 and 9.3 μmol g−1 d−1 for NO3−, 0.1 and 11.1 μmol g−1 d−1 for SO42− and 0.1 and 6.2 μmol g−1 d−1 for CO2. Heterotrophic potentials in wetland soils were strongly correlated with inorganic N and several available C indices (total, dissolved and microbial C), but not with pH or dissolved nutrients (P, Ca2+, Mg2+, Fe(II)). Microbial activity–soil property relationships determined in this study may be useful for predicting the fate of pollutants that are influenced by microbial oxidation–reduction reactions in different types of wetland soils.