Recalcitrant organic matter

Recalcitrant organic matter, metabolic stability, and photolysis... 13... 

Decomposition of organic substrates involves both labile and recalcitrant organic matter, the latter comprising the bulk of the DOC. Turnover of labile pool is very rapid and often may approach a rate of 5-10 times per day thus, actual concentration (storage) of labile DOC is very low (DeBusk and Reddy, 1998). 

A range of extractants and extraction procedures has been used to extract phenolic acids from soil (Dalton 1999). Many of these extractants and extraction procedures, however, recover phenolic acids that are not directly involved in plant-plant allelopathic interactions (e.g., phenolic acids sorbed in the recalcitrant organic matter). Thus considerable efforts were made to identify extraction procedures that would provide reasonable estimates of available phenolic acids ( free phenolic acids in soil solutions and reversibly sorbed phenolic acids on soil particles) in soils (Dalton et al. 1983, 1987, 1989a, b Blum et al. 1994 Blum 1997 Dalton 1999). 

Since the water content and solutions added to soil samples was determined and known, respectively, free , reversibly sorbed, and available phenolic acids of a soil sample could be expressed in either p,M or p,mol/g soil. In addition since under laboratory conditions the concentrations of phenohc acids added to sterile soils were known, the amount (% or p,mol/g soU) of irreversibly sorbed phenohc acids (e.g., bound into recalcitrant organic matter or onto clay minerals) could also be estimated. 

Phenolic acids in soils occur either in a free state in the soil solution, reversibly sorbed to soil particles, fixed (irreversibly sorbed) very tightly to soil particles (e.g., recalcitrant organic matter, and clays), and/or on and in living and dead plant tissues/residues ( free , reversibly sorbed, and fixed). Of general interest to plant-plant allelopathic interactions are the free and reversibly sorbed states frequently referred to as the available fraction. Of particular interest is the active fraction of available phenolic acids, the fraction of available phenolic acids that actually interact with seeds, roots and microbes. Unfortunately we presently do not have a means of quantifying the active fraction, thus the focus on the available fraction. 

Con 4 Phenolic acids were rapidly and irreversibly sorbed to soil particles and/or incorporated into the recalcitrant organic matter within the soil. 

Angelidaki 1, Ahring BK (2000) Methods for increasing the biogas potential from the recalcitrant organic matter contained in manure. Water Sci Technol 41 189-194... 

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