Behavior of phenolic substances in the decaying process of plants

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Abstract
The characteristics of phenolic substances in humic acids prepared from either fresh or 1.5 year-old decayed rice straw samples and from kaolinic soil taken from a paddy field to which rice straw compost had been supplied continuously, and in purified milled wood lignin of rice straw, were investigated by degradation of these substances, with KOH. The amounts of phenolic substances in the humic acids and in the lignin were also compared. The results are as follows: 1) These humic acids contained phenolic moieties ranging from about 8 to 14% in the order of rice straw <soil <decayed straw. The amount of organic solvent-extractable phenolics was about 70% of total phenolics in the humic acid of rice straw, but only about 30% in the humic acids of decayed Itraw and soil. 2) Degradation of these humic acids, their organic solvent-extractable and -unextractable fractions, and isolated rice straw lignin by heating with KOH yielded p-hydroxybenzoic, vanillic, protocatechuic, Iyringic, gallic, and 3,4-dihydroxy-5-methoxybenzoic acids, but neither phloroglucinol nor resorcinol which are normally derived from flavonoid compounds were present. 3) The total amounts of individual phenolic acids ranged from 2 to 4% in these humic acids. The ratios of the amount of each phenolic acid to the total phenolic content were quite similar among humic acids derived from the soil and from decayed and undecayed straw samples, but the ratios were a little different in the case of the isolated lignin and largely different between organic solvent-extractable and -unextractable humic acids.