Carbon compounds recalcitrance

External Direct Indirect Selective translocation of SOM leads to enrichment either of less or of more recalcitrant SOM Rapid depletion of nutrients and labile carbon compounds shortly after defecation leads to an increase in recalcitrant components... 

Fig 3.7. Substrates used by fungi. The is an approximation to the relative number of species that can use the different types of carbon sources. Most fungal species can use monosaccharides. Few fungi can use the single carbon compounds like methane and few fungi can break down the very large and recalcitrant polymer lignin. 

Soil. A Pseudomonas sp. (ATCC 29354), isolated from parathion-amended treated soil, degraded 4-nitrophenol to 4-nitrocatechol, which was recalcitrant to degradation. In an unsterilized soil, however, p-nitrocatechol degraded to nitrites and other unidentified compounds (Sudhakar-Barik et al, 1978a). Pseudomonas sp. and Bacillus sp., isolated from a parathion-amended flooded soil, degraded 4-nitrophenol (parathion hydrolysis product) to nitrite ions (Siddaramappa et al, 1973 Sudhakar-Barik et al., 1976) and carbon dioxide (Sudhakar-Barik et al., 1976). 

The transformation of plant detritus into stabilized humic substances is one of the most complex and least understood biogeochemical processes in the carbon cycle (Stevenson, 1994). Traditionally, decomposition and humification of plant residues was thought to be dominated by the mineralization of labile materials, while more recalcitrant aromatic compounds accumulate in the soil. The application of modem analytical techniques—including solid-state NMR spectroscopy, pyrolysis gas chromatography, and degradative chemical techniques—to the study of decomposition and humification has significantly altered this simple view of carbon transformation in the soil (Baldock et al., 1997 Kogel-Knabner, 1997). 

Other effects Internal Direct Direct and indirect Selective ingestion of less recalcitrant compounds leads to the enrichment of recalcitrant SOM Degradation of more labile compounds in the gut gradually increases the average recalcitrance of nonassimilated carbon... 

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