Synthesis and characterization of specifically C-14-labeled humic model compounds for feeding trials with soil-feeding termites

The feeding activity of soil-feeding termites is considered an important fa ctor in the turnover of soil organic matter in tropical ecosystems, but the nature of the components exploited as carbon and energy source and the con sequences of the gut passage for the residual fraction are still largely ob scure. In order to determine mineralization rates of specific components in feeding experiments, we prepared C-14-labeled synthetic humic model compou nds by peroxidase-initiated radical polymerization of a mixture of phenolic compounds, peptides, amino acids, and carbohydrates. A general characteriz ation of the polymerization products showed that they resembled natural hum ic substances prepared from tropical soil used in feeding trials with soil- feeding termites in their elemental content, infrared spectra, and molecula r weight distribution. Solubility-based fractionation of chemically identic al preparations, arising from selective labeling of different precursors, r evealed that almost all of the label stemming from the protein precursors a nd approximately two-thirds stemming from the peptone and catechol precurso rs were recovered in the humic acid fraction. In contrast, the label of glu cose or glycine was recovered almost completely in the acid-soluble fractio n. High-performance gel-permeation chromatography (HP-GPC) of the humic and fulvic acid fractions combined with online radiotracer analysis showed lar ge differences in the size distribution of the radiolabel, which depended s trongly on the chemical nature of labeled precursor. (C) 2000 Elsevier Scie nce Ltd. All rights reserved.