Decomposition abiotic

Abiotic decomposition can be referred to as physical processes attacking the detrital matter, which may include 

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The fate of triazine herbicides in soils is controlled by three basic processes transformation, retention, and transport. This chapter focuses primarily on soil properties and processes that influence retention. While transformation includes both biological and abiotic decomposition, only abiotic processes are covered in this chapter. 

Ocean DMS is primarily formed by the enzymatic cleavage of dimethylsulphonium propionate (DMSP), which is several orders of magnitude faster than the abiotic decomposition of DMSP Dacey and Blough, 1987). 

Many allelochemicals are decomposed in soil, either abiotically (37) or by microorganisms (95-100). Obviously, the attainment of active concentrations of allelochemicals in soil depends on the relative rates of addition and inactivation. It is important to understand also that microbial decomposition of allelochemicals does not necessarily result in a decrease in allelopathic activity. In fact, the reverse may be true. Hydrojuglone is oxidized in soil to juglone, a quinone that is inhibitory to some species at a 10 ° M concentration (101). Isoflavonoids produced by red clover are decomposed to even more toxic phenolic compounds (95) and to repeat, amygdalin from peach roots is changed to hydrogen cyanide and benzaldehyde which cause the peach replant problem (88), and phlorizin from apple roots is decomposed to several phenolic compounds that appear to be responsible for the apple replant problem (100). 

The term biochemical stabilization refers to the biotic or abiotic production of organic substances that are refractory to decomposition by microorganisms and contribute, through condensation and complex formation, to the stabilization of otherwise easily decomposable substrates such as enzymes. This stabilization process coincides with the process of humification. 

A cadaver exposed to the environment is subject to degradation by various types of animals, of which insects are often the most predominant. Insects can affect the breakdown of the corpse by augmenting the internal decomposition process (Campobasso, Di Vella, and Introna 2001). The succession and development of some insects that visit a corpse can be used to estimate PMI. Succession data are useful in providing a minimum and maximum estimate of time since death. However, biotic and abiotic factors are known to influence carrion insect growth and activity and need to be considered when estimating PMI (Wells and Lamotte 2001). 

In this section, we will consider the effects of soil texture and soil nutrient status on decomposition. The initial stages of leaf litter decomposition will be at least partially decoupled from control by edaphic properties of the soil environment. For example, Scott et al. (1996) found that while SOM decomposition varies significantly with soil texture, the CO2 evolution from surface litter does not. However, as partially decomposed litter is incorporated into the soil both through abiotic and biotic means, the physical characteristics of the soil begin to play an important role in the overall degradation and stabilization of the organic inputs. 

Meentemyer (1995) asked the question Is the chmate of decay processes measured at weather stations The microclimate at the scale of an individual leaf may be nearly fully decoupled from what a nearby weather station measures. For field studies following decomposition processes at short time intervals, this decoupling may have important consequences. However, for smdies comparing annual mass losses across large geographic regions, the average climate at the weather station will probably suffice. Additionally, as Lavelle et al. (1993) noted, climate is not an equally important constraint across all ecosystems. Whitford (1989) hypothesized that abiotic controls on decomposer food webs are least important in moist, closed-canopy forests and most important in hot deserts. 

Nitric oxide and N2O are also produced abiotically by chemical decomposition of NO2 (Hooper and Terry, 1979). The reaction is favorable at low pH and yields mainly NO (van Cleemput and Baert, 1984), although N2O can also be produced (Martikainen and De Boer, 1993). Abiotic production of NO and N2O is assumed to be relatively unimportant in most ecosystems (e.g., Webster and Hopkins, 1996). 

Demethylation in the water column and sediments is receiving increasing attention. Both abiotic (e.g.. Sellers et al., 1996, 2001) and biotic (e.g., Pak and Bartha, 1998 Marvin-Dipasquale and Oremland, 1998 Marvin-Dipasquale et al., 2000 Hintehnann et al., 2000) processes are imphcated. The result is that MMHg accumulation in aquatic systems represents a balance between methylation, bioaccumulation, and the demethylation processes. In sediments, MMHg decomposition is particularly important, and it is possible that some sediments represent net sinks, rather than net sources, for MMHg in the water column. 

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