Soil organic carbon chemical stabilization

Rumpel, C., Eusterhues, K., and Kogel-Knabner, I. (2004b). Location and chemical composition of stabilized organic carbon in topsoil and subsoil horizons of two acid forest soils. Soil Biol. Biochem. 36,177-190. 

The increase in atmospheric COi because of fossil fuel emissions has been identified as a major driving force for global climate change. Soil organic matter (SOM) is expected to be an important sink for this carbon (Ciais et ciL, 1995 Schimel, 1995 Steffen et aL, 1998). However, at higher mean temperatures, this sink may act as additional source for CO2 if it is accessible to microbial decomposition. To understand these complex interactions between stabilization and decomposition of SOM, it is crucial to investigate not only the turnover and stability, but also the chemical nature of soil organic matter. 

In terms of improving our ability to predict soil C turnover, we identify five priorities for research (1) The interactive effects of temperature and moisture on microbial decomposition rates, because soils will experience novel and transient conditions (2) the mechanisms governing protection of OM through interactions with mineral surfaces and due to spatial structure (3) the mechanisms leading to slower OM turnover times with depth (4) the potential for nonlinear responses of decomposition to C availability—for example, the role of labile C inputs in stimulating decomposition of less labile OM (i.e., priming) and density-dependent microbial behavior and (5) how the chemical characteristics of organic compounds, as inputs from different plant species, charred (black) carbon, or microbial cell walls and by-products, influence mechanisms of stabilization and turnover. 

The redox potential-pH stability diagram (Figure 12.11) indicates that between pH 7 and 8, zinc carbonate (ZnCOj) is formed when the concentration of dissolved carbon dioxide (CO2) is 10 mol L . At low redox values, zinc sulfide is the most stable combination. Zinc precipitation by the hydrous metal oxides of manganese and iron is the principal control mechanism for zinc in wetland soils and freshwater sediments. The occurrence of these oxides as coatings on clay and silt enhances their chemical activity in excess of their total concentration. The uptake and release of the metals is governed by the concentration of other heavy metals, pH, organic and inorganic compounds, clays, and carbonates. 

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