Dynamics of low-molecular-weight aliphatic carboxylic acids (lacas) in forest soils

Abstract

By improving the existing methods for quantifying organic acids in paddy soils, we developed a quantitative analytical method for low-molecular-weight aliphatic carboxylic acids (LACAs) in forest soils. Appropriate pre-treatment and concentration of soil extracts in combination with HPLC analysis where two types of columns and detectors were introduced enabled to obtain a sensitive determination of LACAs in forest soils. Moreover, choice of extractant enabled us to differentiate the existing forms of LACAs, namely water-soluble and adsorbed ones, the latter reflecting the difference between the phosphate buffer-soluble and water-soluble forms. By applying this method to the upper parts of the A and B horizon samples from a Podzolic soil, two Brown Forest soils and two Andosols, the following results were obtained. 1) Comparison between the upper part of the A and B horizons of each soil profile indicated that fairly comparable amounts of LACAs were present in the B horizon as well as A horizon. 2) In the upper part of the A horizon, the vegetation played a major role in the amount and composition of LACAs to some degree, irrespective of the differences in parent materials. 3) As for the samples from the two Andosols, the contents of volatile LACAs, mainly formic acid and acetic acid, increased with the increase in the moisture content, and also the contents of adsorbed LACAs, mainly oxalic acid, increased with the increase in the amorphous Al and Fe contents. 4) The total amount of water-soluble LACAs, especially non-volatile LACAs, strongly affected the soil solution pH of different types of forest soils.