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

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Abstract
We examined the seasonal changes in the amounts and composition of low-molecular-weight aliphatic carboxylic acids (LACAs) in an AndisoS of Japan. Determination of ten kinds of LACAs was conducted for the 18 soil samples which were collected from Ah1 and Bw1 horizons of one identical profile for a duration of 1 y. The total amount of LACAs which ranged from 184.7 to 324.7 μmol kg-1 and from 131.5 to 260.3 μmol kg-1 in the Ah1 and Bw1 horizons, respectively was larger in the Ah1 horizon than in the Bw1 horizon for almost all the periods. The total amount of LACAs in the Ahl horizon reached maximum values at the beginning of July, when both soil temperature and moisture content were high. The seasonal changes in the amount of volatile LACAs (VCAs), mainly formic acid and acetic acid, were relatively similar to those in total LACAs, while there were two peaks in the amount of nonvolatile LACAs (NVCAs), dominated by oxalic acid and citric acid. As for the Bw1 horizon, although the total amounts of LACAs tended to be larger in July, the seasonal changes in the total amounts of VCAs and NVCAs were not distinct. The total amount of water-soluble LACAs was larger in the Bw1 horizon than in the Ah1 horizon in about half of the year-long experiment, suggesting that LACAs were transported from the Ahl to Bw1 horizon with higher precipitation and/or the production of VCAs in the Bw1 horizon when both the soil temperature and the moisture content were high.