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 SO₄/^2- 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.