STABILIZATION IN HUMUS AND INCORPORATION INTO BIOMASS OF A WIDE VARIETY OF ORGANIC COMPOUNDS DURING BIODEGRADATION IN SOIL

The effect of soil type and incubation period on the biodegradation, incorporation into biomass and stabilization in humus of specific carbons of ferulic, p-hydroxycinnamic and benzoic acids; of ('14)C-labeled cornstalk and/or wheat straw lignin, polysaccharide, and protein fractions, and whole wheat straw; of ('14)C-labeled catechol, 4-chlorocatechol, and 4,5-dichlorocatechol, free and linked into model humic acid polymers, and 2,4-D, glucose and a fungal melanin were followed over one year. Biomass was estimated by the fumigation method.; Catechol, 4-chlorocatechol and 4,5-dichlorocatechol readily linked into model peroxidase humic acid type polymers, with 84-96% recovery of the ('14)C-activity in the reaction mixtures. 4,5-dichlorocatechol was the least reactive. 2,4-D did not link into the polymers.; The rate and extent of degradation depended upon the substrate, the concentration, and the soil. Substrates such as 2,4-D, the protein and polysaccharide fractions of cornstalk or wheat straw, ferulic acid and glucose were readily degraded with up to 85% of the labeled C being evolved in one year. The most rapid rate of degradation took place during the first few weeks of incubation. In contrast, only 38-50% of the catechol, 22-63% of the 4-chlorocatechol, and 22-62% of the 4,5-dichlorocatechol carbons were lost over one year indicating substantial stabilization of these compounds, probably by enzymatic polymerization reactions. Catechol, 4-chlorocatechol, and 4,5-dichlorocatechol incorporated into model polymers were still more stable with 6-22%, 8-42% and 13-43% respectively of the ('14)C evolved as CO(,2).; In general, greater amounts of CO(,2) were evolved from the neutral and alkaline soils (pH 7.0, 7.4, 7.8) than from the acid soils (pH 5.0, 5.5). More residual C was stabilized into humic acid in the acidic soils than in the neutral soils. The greater the amount of ('14)C evolved as CO(,2), the greater the amount of the residual ('14)C that was found in the biomass. After the period of rapid degradation, the amount of residual carbon found in the biomass decreased with time.