Biodegradation of 14C-labeled model and cornstalk lignins, phenols, model phenolase humic polymers, and fungal melanins as influenced by a readily available carbon source and soil

Abstract

After 6 months of incubation in a fertile neutral sandy loam, about 48% of the ring carbons and 2-carbons and 60% of the OCH3 carbons of specifically labeled coniferyl alcohol had evolved as CO2. After 1 year, corresponding values were 55 and 65%. When coniferyl alcohol units were linked into model and cornstalk lignins, about 23% of the ring carbons and 2-carbons and 39% of the OCH3 carbons had evolved as CO2 after 6 months. After 1 year, corresponding values were about 28 and 46%. The addition of orange leaves (0.5%, wt/wt) after 6 months did not significantly increase the evolution of 14CO2. Addition of orange leaves (0.5%, wt/wt) with specifically 14C-labeled pyrocatechol, coumaryl alcohol, model lignins, humic acid-type phenolic polymers and of uniformly 14C-labeled fungal melanins did not increase labeled C losses or C losses from the orange leaves. Decomposition of protein and pyrocatechol linked into model humic acid polymers, coniferyl alcohol C in model lignins, and Eurotium echinulatum melanin in six soils varied from 2 to 14%. Significant differences in C losses were related to soils and were not influenced by orange leaf applications.