Studies on soil polysaccharides. III. Composition of polysaccharides in some Australian soils

Abstract

Aldoses released by acid hydrolysis from soils, light fractions, soil extracts, and gel chromatographic fractions of the extracts were determined by gas-liquid chromatography. The results show that different soils contain different amounts of aldoses and these represent from 5 to 17% of the organic matter. Eight to 26% of the aldoses in soils was extracted by a pretreatment with 1N HCl; 25-55% by a subsequent shake in 0.5N NaOH, and a further 4-24% by a second treatment with 0.5N NaOH (ultrasonic dispersion). A final treatment of the soil with acetic anhydride containing H2SO4 extracted a further 8-29 % of the aldoses. From 4 to 35 % of the soil polysaccharides was not extracted by the four sequential chemical treatments. In the acid extracts of the soils, mannose dominated high molecular weight fractions, but glucose was dominant in smaller molecules. The sugar compositions of the NaOH extracts from different soils were similar, glucose representing about a third of the sugars present. The non-extracted polysaccharides and those extracted by the acetylation procedure were rich in glucose and considered to be from plant remnants not previously removed in the light fraction. It was concluded that the monosaccharide composition of different soils is very similar and that most of the differences in relative amounts of monosaccharides are associated with glucose, arabinose, and xylose which are probably present in plant fragments. These three sugars tend to be dominant in soils rich in plant remnants.