World Congress of Soil Science Logo 18th World Congress of Soil Science
July 9-15, 2006 - Philadelphia, Pennsylvania, USA
International Union of Soil Sciences

Monday, 10 July 2006 - Friday, 14 July 2006

This presentation is part of 141: 2.3B Molecular Approaches to Microbial Ecology in Soils - Poster

Soil Chemistry and Bacterial Sulfur Oxidation in Naturally Metalliferous Peat Soils.

Tarah S. Sullivan, Janice Thies, and Murray McBride. Cornell Univ, 706 Bradfield, Crop and Soil Sciences Dept, Ithaca, NY 14853

Naturally occurring peat soils in Western NY contain anomalously high concentrations of Zn, Cd, and S. In some cases, total soil Zn has been reported near 88,000 mg/kg and zones of Zn phytotoxicity are frequently reported throughout the area. Under anoxic conditions, metal sulfides are relatively insoluble and immobile and therefore pose little threat to the biota of the system. However, when these agricultural peat fields are drained for planting every spring, thus aerating the system, the metal sulfides become oxidized and release sulfates along with free Zn and Cd into the soil solution in bioavailable forms. High metal concentrations in the soil solution can cause phytotoxicity in specific areas and, if leaching occurs, can contaminate downstream surface waters. Preliminary data on oxidation kinetics of these two sulfides suggest that CdS is much more susceptible to chemical oxidation under controlled laboratory conditions than is ZnS (sphalerite), which was relatively stable to oxidation under the same conditions. When these peats are exposed to a drying event, concentrations of dissolved organic carbon increase simultaneously with increases in the concentrations of free Zn and Cd. These observations combined with the fact that this sphalerite is relatively stable to chemical oxidation suggest strongly that the soil microbial community is playing a significant role in the oxidation of ZnS and CdS and the subsequent release of free Zn and Cd under aerobic conditions. Although the research on this site to date suggests indirectly that microbial activity is responsible for this key process, no study has focused on the soil microbial sulfur oxidation pathway presumably responsible. Biological oxidation of sulfur compounds is fairly widespread in soil and water microbial communities and there is a great deal of diversity in the phylogeny and physiology of the microbes capable of sulfur oxidation. The biochemical reactions in sulfur oxidation pathways are performed by aerobic chemotrophic and anaerobic phototrophic bacteria, as well as Archaea. When the resolving power of T-RFLP is used in combination with functional or marker genes, such as sulfur oxidation via the PSO pathway (soxB), we may begin to understand better the community structure differences observed across the soil Zn, Cd and S concentration gradients at this site. In this study, spatial and temporal variations in available soil Zn and S across an agricultural field in upstate NY were highly correlated with Bacterial 16S T-RFLP fingerprints as well as the sulfur oxidizing microbial community (as measured by T-RFLP fingerprinting of soxB gene amplicons). These results help begin to explain the mechanisms involved in metal cycling at this site.

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