Study of free and occluded particulate organic matter in soils by solid state 13C Cp/MAS NMR spectroscopy and scanning electron microscopy

作者：Ali Golchin, JM Oades, JO Skjemstad, Philip Clarke · 发表于：Soil Research · 年份：1994 · DOI：10.1071/sr9940285 · 被引用次数：835 · 研究领域：Soil Carbon and Nitrogen Dynamics、Isotope Analysis in Ecology、Agriculture, Soil, Plant Science

A simple densimetric method for the separation of free and occluded particulate organic materials was developed and applied to five virgin soils. The free organic matter was isolated by suspending the soil in sodium polytungstate solution (d = 1.6 Mg m-3) and decanting the light material. The remaining soil was disaggregated by sonification for liberation of occluded organic materials. The free light fraction consisted of large, undecomposed or partly decomposed root and plant fragments. This fraction comprised 0.59-4.34% of soil dry weight and accounted for 6.9-31.3% and 5.9-22.1% of total soil carbon and nitrogen respectively. Identifiable components of the occluded fraction were small particles of incompletely decomposed organic residues, pollen grains, particles of plant tissue such as lignin coils and phytoliths. This fraction comprised 0.69-1.81% of soil dry weight and represented 9.2-17.5% and 6.2-14.1% of the total soil carbon and nitrogen. The proportion of soil organic carbon recovered as the occluded fraction was high in soils with high clay contents. The chemical composition of occluded and free organic materials was investigated by solid-state 13C CP/MAS NMR spectroscopy. Despite the differences in soils, environmental conditions and vegetation, the organic structure of the free light fraction was similar in four of the five soils. This fraction consisted of 55-63% O-alkyl C, 18-25% alkyl C, 14-18% aromatic C, and 5-7% carbonyl C. In the other soil, this fraction...