Phenolic acid soil adsorption

The nature of soil-phenolic acid interaction adsorption-desorption. Adsorption of a solute from solution onto a solid matrix results in a higher solute concentration at the fluid-solid interface than in the solution. Huang and coworkers (27) observed a high sorption capacity of the mineral fraction of four latosols for phenolic acids. On the basis of their results, distribution coefficients,... 

T. Makino, Y. Takahashi, Y. Sakurai. and M. Nanzyo, Influence of soil chemical properties on adsorption and oxidation of phenolic acids in soil suspension. Soil Sci. Plant Nittr. 42 U1 (1996). 

Approximately 40 to 50% of the total amount of phenolics sorbed was retained by the organic matter fraction (27). In surface soil layers, organic matter is frequently intimately associated with the mineral components present, providing a large surface area and reactive sites for surface interaction. Soil acidity has a major influence on phenolic adsorption by the organic carbon fraction, since the degree of dissociation of the phenolic acids is pH-dependent. Whitehead and coworkers (28) observed that the extractability of several phenolic acids was highly dependent upon the extractant pH between pH 6 and 14. The amount extractable continually increased with extractant pH thus the extracted acids could not be readily classified into distinct fractions. 

As said above, plant root chemistry may also influence deeply alpine soil microorganism s biomass. It turns out that the particular chemical composition of exudates is a strong selective force in favour of bacteria that can catabolize particular compounds. Plants support heterotrophic microorganisms by way of rhizodeposition of root exudates and litter from dead tissue that include phenolic acids, flavonoids, terpenoids, carbohydrates, hydroxamic acids, aminoacids, denatured protein from dying root cells, CO2, and ethylene (Wardle, 1992). In certain plants, as much as 20-30% of fixed carbon may be lost as rhizodeposition (Lynch and Whipps, 1990). Most of these compounds enter the soil nutrient cycle by way of the soil microbiota, giving rise to competition between the myriad species living there, from microarthropods and nematodes to mycorrhiza and bacteria, for these resources (e.g. Hoover and Crossley, 1995). There is evidence that root phenolic exudates are metabolized preferentially by some soil microbes, while the same compounds are toxic to others. Phenolic acids usually occur in small concentration in soil chiefly because of soil metabolism while adsorption in clay and other soil particles plays a minor role (Bliun et al., 1999). However, their phytotoxicity is compounded by synergism between particular mixtures (Blum, 1996). 

Lyu S-W, Blum U (1990) Effects of fendic acid, an adelopathic compound, on net P, K, and water uptake by cucumber seeddngs in a split-root system. J Chem Ecol 16 2429-2439 Lyu S-W, Blum U, Gerig TM, O Brien TE (1990) Effects of mixtures of phenolic acids on phosphorus uptake by cucumber seedlings. J Chem Ecol 16 2559-2567 MaMno T, Takahashi Y, Sakurai Y, Nanzyo M (1996) Infiuence of soil chemical properties on adsorption and oxidation of phenodc adds in sod suspension. Soil Sci Plant Nutr 42 867-879... 

Figure 11 shows the relative adsorption of 14 different herbicides by soil organic matter. The acidic herbicides, dinoseb, picloram, 2,4-D, and dicamba, were adsorbed in relatively low amounts compared with the basic and cationic herbicides, and the adsorption amount was inversely related to the water solubilities of the acidic compounds (Table IV). The weakly acidic phenol, dinoseb pKa = 4.40), was adsorbed more than the stronger acids, picloram pKa = 1.90), 2,4-D pKa = 2.80), and dicamba pKa = 1.9). Since the organic matter was an acidic muck... 

SHINDO H. and KUWATSUKA S. 1976. Behavior of phenolic substances in the decaying process of plants. IV. Adsorption and movement of phenolip acids in soils. 

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