Changes in composition of soil polysaccharides and aggregate stability after carbon amendments to different textured soils

Changes in the composition of soil polysaccharides, after amendment and incubation of different textured soils with either ground wheat-straw or glucose, were studied in relation to microbial activity and aggregate stability. Analyses of free and soil (straw)-bound saccharides were carried out by high performance anion exchange chromatography with pulsed amperometric detection (HPLC-PAD). Eighty-five percent of the added glucose was respired after 15 days of incubation (15°C). Metabolism of the glucose amendment did not affect the total soil saccharide content of a loamy sand during the course of the experimentation period. By contrast, total soil saccharides declined to approximately 50% of the unamended (control) silty loam. In the straw treatments, more of the straw saccharides remained in the loamy sand (54.9%) than in the silty loam (26.4%) after 15 days of incubation. At the end of the experiment (after 220 days) the saccharide concentrations of both treatments had approached those of the unamended control soils. The monosaccharide content of soils followed the same trend in most cases, these concentrations reflecting the degradation process in the straw amendment treatments. Mannose apparently was synthesized by soil microorganisms. Glucose and straw metabolism led to a significant increase in aggregate stability in the three soils during the incubation time. Independent of the clay content of the soils, aggregate stability was still pronounced together with an increased microbial biomass level (straw treatment only) after 220 days. However, no direct link between a specific monosaccharide content and aggregate formation or stability could be shown. Polysaccharide production seemed to be related to C-availability or C over-supply.