Effects of tree species and soil physico-chemical conditions on the nature of soil organic matter

Abstract

Forty-one properties of the organic matter in surface soil samples collected under oak (intermediate between Quercus petraea and Q. robur) and yew ( Taxus baccata) growing on soils overlying slate and limestone in N.W. England were studied using analysis of variance. Total C, N, polysaccharides, and lipids, the amount of C extracted, and the amount of humic acid C, fulvic acid C, and of the C in the polyphenol fraction of the fulvic acid were related more to the amount of organic matter in a sample than to its chemical nature. The greater C-to-LOI and C-to-N ratios of the samples collected on slate were consistent with different types of transformation of litter compounds by organisms in the soils. The lipid-to-LOI ratio appeared to be lower in soils with high biological activity. The type of humification on limestone was associated with lower ratios of humic acid carbon-to-fulvic acid carbon and a larger percentage of the carbohydrate fraction in fulvic acid, and a larger proportion of the total C was in polysaccharides. The loss of vanillyl units from plant lignin was greater under yew with no significant effect of geology, while the greatest loss of syringyl units occurred under yew on slate. There were statistically-significant, but numerically small, differences in the compositions of the humic acids, the clearest differences being a greater C-to-N ratio and lower N-to- S ratio on slate. The E 4-to-E 6 ratios were correlated positively with humic acid O and O-to-C ratio, which suggests that the ratio decreases with an increase in the degree of condensation.