Soil organisms, terrestrial decomposition

Though the body itself forms the primary decompositional site, the soil beneath it may be equally important. Corpses located in outdoor environments on a terrestrial surface create an interface within which soil fauna and carrion-dwelling organisms interact. The interactions in this zone are affected by soil type, vegetation, decomposition of the corpse, and a variety of environmental factors. Apart from the work by Bornemissza (1957) and Lundt (1964) the succession of insects in this interface, and within the soil itself, has been largely overlooked in the literature, and the forensic implications have yet to be considered. 

Among the carbon reservoirs of the biosphere, a large proportion is stored in soil organic matter and marine sediments (Bolin, 1977). The accumulation of carbon in soils and sediments is a function of the organic carbon balance between net primary production (carbon fixation) and heterotro-phic metabolism (decomposition). The fixation of atmospheric carbon through photosynthesis is the major sonrce of carbon to terrestrial, wetland, and aquatic ecosystem. 

Abrahamsen, G, J. Hovland, and S. Hagvar. 1979. Effects of artificial acid rain and liming on soil organisms and the decomposition of organic matter. Paper presented at NATO Advanced Research Institute, Effects of Acid Precipitation on Terrestrial Ecosystems, Toronoto, May 22-26. (In Press)... 

Because of their often high biological productivity and low rates of decomposition under anoxia, wetlands are one of the largest terrestrial sinks for carbon. They account for about a third of the soil carbon globally (Table 1.4). However there are large differences between wetland types. Organic wetland soils tend... 

NOM is common in sediments, soils, and near ambient (<50 °C) water. The materials result from the partial decomposition of organisms. They contain a wide variety of organic compounds, including carboxylic acids, carbohydrates, phenols, amino acids, and humic substances (Drever, 1997, 107-119 Wang and Mulligan, 2006, 202). Humic substances are especially important in interacting with arsenic. They result from the partial microbial decomposition of aquatic and terrestrial plants. The major components of humic substances are humin, humic acids, and fulvic acids. By definition, humin is insoluble in water. While fulvic acids are water-soluble under all pH conditions, humic acids are only soluble in water at pH >2 (Drever, 1997, 113-114). 

In their now classic text on decomposition in terrestrial ecosystem, Swift et al. (1979) outlined three broad groups of factors that govern decomposition of organic residues in soils. The three groups of factors are the resource (or substrate) quality of the organic residue, the environmental factors, and the presence and activity of decomposer organisms. 

An alternative to the terrestrial synthesis of the nucleobases is to invoke interstellar chemistry. Martins has shown, using an analysis of the isotopic abundance of 13C, that a sample of the 4.6 billion year old Murchison meteorite which fell in Australia in 1969 contains traces of uracil and a pyrimidine derivative, xanthine. Samples of soil that surrounded the meteor when it was retrieved were also analyzed. They gave completely different results for uracil, consistent with its expected terrestrial origin, and xanthine was undetectable [48], The isotopic distributions of carbon clearly ruled out terrestrial contamination as a source of the organic compounds present in the meteorite. At 0°C and neutral pH cytosine slowly decomposes to uracil and guanine decomposes to xanthine so both compounds could be the decomposition products of DNA or RNA nucleobases. They must have either travelled with the meteorite from its extraterrestrial origin or been formed from components present in the meteorite and others encountered on its journey to Earth. Either way, delivery of nucleobases to a prebiotic Earth could plausibly have been undertaken by meteors. The conditions that formed the bases need not have been those of an early Earth at all but of a far more hostile environment elsewhere in the Solar System. That environment may have been conducive to the production of individual bases but they may never have been able to form stable DNA or RNA polymers this development may have required the less extreme conditions prevalent on Earth. 

In general, soluble forms of iodine seem to be easily available to plants therefore, terrestrial plants contain much less iodine than do marine plants, which are known to concentrate iodine from 50 to 8800 mg kg DM (Shaklette and Cuthbert 1967). Organically bound iodine is scarcely available to plants soil iodine becomes available after the decomposition of organic matter by bacteria (Selezniev and Tiuriuka-nov 1971). Atmospheric iodine also contributes to the iodine content of plants (Kabata-Pendias and Pendias 1992), as plants can... 

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