, Volume 76, Issue 1-3, pp 197-212

Anaerobic processes in soil

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Summary

Anaerobic conditions in soil affect plant productivity as well as organic matter and nutrient dynamics. Anaerobic processes often dominate biological and chemical features of flooded and poorly drained soils but in well-drained soils, anoxia is restricted to small zones and to limited periods. The anaerobic processes listed according to their approximate sequence of occurrence as the redox decreases are: Fe3+ and Mn4+ reduction, denitrification, fermentation, nitrate respiration, dissimilatory nitrate reduction to ammonium, sulfate reduction, carbon dioxide reduction, acetate splitting, and proton reduction. Two of the anaerobic processes, denitrification and fermentation of pollutant chemicals have been studied and recent results are summarized here. We describe the measurement of denitrification using a recirculating atmosphere of acetylene, provide quantitative information on the effect of moisture and oxygen on denitrification, and report on the oxygen concentration within soil aggregates measured by oxygen microelectrodes. The current hypotheses for the pathway leading from nitrate to the N−N bond and N2O are also presented. Recent work in our laboratory has shown a new reaction for the metabolism of some chlorinated organic chemicals. In this reductive dehalogenation, the ring Cl is replaced by a proton. An unusual organism which carried out this reaction has been enriched and isolated on 3-chlorobenzoate. These anaerobic reactions may be of further use in pollutant removal. With these new techniques and knowledge available, it is now possible to gain a better understanding of the biochemistry, physiology, ecology and diversity of the anaerobic organisms and their processes in soil.

Keynote address