There are different types of phenolic compounds in the soil, mainly from plants or roots, but I don't know if these can drive in different ways depending on their molecular structure or if that is indifferent.
generally these molecules are very poor sources of energy, and require high-energy, specialised enzymes (e.g. phenol oxidase) to degrade. The side chains and functional groups (e.g. carboxyl) are easily cleaved and used, however the phenol units and aggregated molecules can accumulate. This is typically observed in peatlands and mor humus forms in boreal forests. There are more labile phenolics though, generally those exuded from roots, and leached from litter. The majority of these, as I mentioned, are subject to some degree of oxidation, and removal of side chains (COOH etc) can result in the production of more persistent phenols, such as catechol (C6H6O2). These phenolics are also implicated in metal mobility and podsolisation in general. There is also a difference in the rate and timing of input, considering the root exudation versus that leached by litter. If you have a general search through soil biology and biochemistry, you should come up with some good overview papers and specific studies.
Hope that is a useful start to the discussion
rob
Maybe this link can be useful: http://books.google.es/books?id=kCfkTRf32bAC&pg=PA220&dq=biochemical+pathways+degradation+phenolic+compounds&hl=es&sa=X&ei=eCGiUo-fNbGu7AazoIHoCg&ved=0CDwQ6AEwAQ#v=onepage&q=biochemical%20pathways%20degradation%20phenolic%20compounds&f=false
Seems it can be easily degradable in soil and can enhance or not C turnover depending on the microbial population. The degradation pathway in the link has an step that releases CO2 so degradation could be tracked through CO2 measurements or by calorimetry.
Phenolic compounds are known to inhibit microbial activity in soil for a certain time, depending on temperature by complexing extracellular enzymes. They are held responsible for largely contributing to reduced litter mineralisation in soil under conifers and retarded pomace mineralisation in vineyard soils.
Schimel JP et al (1996) Can J Bot 74:84–90
Valachovic YS et al (2004) Can J For Res 34: 2131–2147
Nendel & Reuter (2007) Nutr. Cycl. Agroecosys. 79 (3), 233 – 241
Fungi are much better at utilizing this material in soils than bacteria, and a strong presence of either white or brown rot will allow this material to contribute to the C cycle. See the following review:
Bugg, T. D., Ahmad, M., Hardiman, E. M., Rahmanpour, R. (2011) Pathways for degradation of lignin in bacteria and fungi. Natural Products Reports 28, 1883-1896
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