Contribution of plant cuticular materials to humic materials in soil.
Elizabeth Johnson, University of Massachusetts, Amherst, 465 Sharon Drive, Cheshire, CT 06410-4241 and Baoshan Xing, "Dep. of Plant, Soil & Insect Scien", "Stockbridge Hall, Univ.of Ma", Amherst, MA 01003, United States of America.
Recent studies indicate that the aliphatic components of soil organic matter (SOM) play an active role as sorbents of organic compounds in soils. A primary source of aliphatic moieties in SOM is the cuticular material derived from plants, including cutin and cutan. Due to its high resistance to degradation, cutan has been identified in fossil plant cuticles, and is believed to contribute to soil humic substances, such as humic acid (HA) and humin (HU). The objective of this study was to assess the potential contribution of plant cuticular materials to humified organic matter in soil by applying the cuticle fractionation method. The isolated fractions from the humic materials and decomposed cuticles were characterized using 13C Solid State MAS NMR, ATR-FTIR, and elemental analysis, and underwent batch sorption experiments with phenanthrene. NMR results confirm that the bulk, dewaxed and saponified fractions of the HA and HU are highly aliphatic and that the acid hydrolyzed fraction (cutan-like residue) has the lowest aliphaticity of the four fractions (~50%) isolated. Elemental analysis data indicate that atomic (O+N)/C atomic ratios were highest in the saponified fraction. Sorption work demonstrates that while Koc values for the HA fractions were slightly below those for the decomposed cuticles, HU values were similar to those for the cuticular materials. Overall, all analyses performed on HA and HU exhibited similar trends to that of the decomposed cuticle, indicating the plant cuticle material is likely to contribute to humic materials in the soil.