Characterization of neutral phosphate buffer extractable soil organic matter by electrophoresis and fractionation using ultrafiltration(Fertilizers and Soil Amendments)

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To characterize neutral phosphate buffer (NPB) extractable organic matter, we determined the properties of NPB extracts by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) from concentrated or fractionated NPB extracts prepared using ultrafiltration membranes and measured the concentrations of organic N, organic C, amino acids and polyphenol in each fraction. The NPB extract was fractionated into three fractions of molecular weight (MW) > 100,000, 30,000-100,000 and 5,000-30,000 Da. As a result of SDS-PAGE, a smear band ranging from small to large MWs was detected in concentrated NPB extracts, and diverse band patterns were detected in the corresponding MWs of each fraction from fractionated NPB extracts. Two-dimensional electrophoresis demonstrated that most of the constituents of the NPB extracts may not have isoelectric points. These results indicate that the NPB extract is a mixture of diverse MW substances with negative charge. The fraction ranging from 5,000 to 30,000 Da was a predominant fraction with respect to the amounts of N and C. The amino acid properties of the NPB extracts were homogenous, regardless of their MWs. Although the NPB extracts contained amino acids, the absorbance detected at 280nm was not because of these, but because of polyphenol. In addition, the similarity of several features of NPB extracts to humus suggests that NPB extract is a humic substance.