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The distribution of lipid sulfur in soils of British Columbia Chae, Yeh Moon

Abstract

The significance of soil lipids to man's environment is not fully yet understood, but there are some indications that suggest possible roles in influencing soil structure, hydrophobicity and infiltration characteristics, phytotoxicity, and nutrient cycling particulargy of P and S. The lipids may also act as a sink for polynuclear hydrocarbons and some pesticides. The present study constitutes the first reported investigation of sulpholipids in soil. The distribution of soil lipid sulfur was studied particularly in relation to the factors which influence the content of the lipid sulfur under different soil environments. Further studies were carried out to fractionate total lipids and lipid sulfur by means of column chromatography and to characterize soil lipid sulfur, using thin-layer and gas-liquid chromatography. The investigation of the distribution of lipid sulfur in soils showed that lipid sulfur was found in all soils examined but the amount was very variable. The lipid sulfur contents were higher in organic horizons than in mineral horizons, and poorly drained soils had higher lipid sulfur than freely drained soils. The highest lipid sulfur content was observed in poorly drained organic soils. The lipid sulfur accounted for a small percentage of total sulfur and of total lipids. The lipid sulfur contents were on average nearly three times higher than the lipid phosphorus contents. The lipid sulfur content was significantly correlated only with total and HI-reducible sulfur and organic carbon content, among various soil factors examined. The distribution of lipid sulfur in soil can be best explained by the two soil factors, i.e., total lipid content and total soil sulfur content, when the lipid sulfur content was expressed as part per million of soil. Therefore, soil factors can be chosen accordingly when a suitable expression for the lipid sulfur content was used for the distribution of the lipid sulfur in soil. The fractionation of soil total lipids, for selected soils, into three general classes, i.e., neutral lipids, glycolipids and polar lipids, on a silicic acid column has shown that the distribution pattern of the three classes of lipids was similar for all eight soils studied regardless of soil type. The uniformity of the distribution patterns suggests that the lipids in these soils were similar in type and origin, or that their distributions were affected by, and made more uniform through, interaction of microorganisms with other soil environmental factors. The soil lipid sulfur, however, had no such a consistent similarity in the distribution pattern, differing from soil to soil. The most significant finding of the study was that significant amounts of sulfur were, in all cases, recovered in each general class, in contrast to the finding that most of the total lipids were recovered in both neutral lipid and glycolipid classes, exclusively. This finding clearly suggests that soil lipid sulfur is present in a variety of forms. Observation of the thin-layer and gas-liquid chromatographic behavior of general lipid classes, fractionated from two soil samples, was conducted to characterize soil lipid sulfur. Thin-layer chromatographic behavior of the corresponding lipid classes of the two soils were not similar to each other, although column chromatographic behavior of the lipid classes of the two soils were similar to each other. These dissimilarities indicate that the individual component of one general lipid class fractionated from one soil differs from that of the other soil. Observation on the gas-liquid chromatographic behavior of general lipid classes suggested that GLC could be used in monitoring the sulfur-containing compounds in lipid extracts of soil by choosing a suitable column, and organic solvents of high purity. Although the attempt to separate and characterize individual sulfur-containing lipid components by chromatographic methods in this last phase of investigation failed to significantly advance our knowledge of individual lipid constituents, partly because of technical problems and partly because of lack of time, it served to re-emphasize the complexity both of soil lipids in general, and of their sulfur-containing constituents in particular. It also indicated some of the more promising lines of investigation for future studies.

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