Due to the deficiency of oxygen in flooded soils, those organisms inhabiting flooded soils must be able to survive with little to no oxygen. Although energy yields are much greater with oxygen than with any other terminal electron acceptor (see #Electron tower theory, section 2.1.1 – “Electron tower”), under anoxic conditions anaerobic and facultative microbes can use alternative electron acceptors such as nitrate, ferric iron (Fe III), manganese (IV) oxide, sulfate, and carbon dioxide to produce energy and build biomass.