BACTERIAL CYCLING OF MINERALS THAT AFFECT PLANT-GROWTH IN WATERLOGGED SOILS - A REVIEW

Plant growth in waterlogged soils may be greatly affected by reduced minerals such as ammonium, manganous and ferrous ions, and sulphide. A more detailed description is given of the microbial and chemical processes that lead to reduced minerals, as well as of the micro-organisms involved. Reduction processes do not occur simultaneously, but consecutively according to a fixed sequence: oxygen, nitrate, manganese (IV) oxide, ferric oxide, sulphate and carbon dioxide. Special attention is paid to the microbial mechanisms of mutual exclusion of reduction processes. Re-oxidation of reduced minerals occurs at the oxic-anoxic interfaces in the flooded soil, i.e. at the oxidized upper layers of the soil and in the oxidized rhizosphere of waterlogged plants with aerenchyma. The micro-organisms involved in the oxidation processes with oxygen are mentioned in relation to their ecological niches. Leakage of oxygen by plants with aerenchyma may be a way to counteract the toxic effects of reduced minerals. The conclusion, however, is that hardly anything is known about the sequence of oxidation processes in the oxidized rhizosphere. © 1990.