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HUMIC MODEL COMPOUNDS; FEEDING TERMITES; MICROBIAL BIOMASS; URIC-ACID; GUT; MATTER; DIGESTION; STABILIZATION; SPECTROSCOPY; MOBILIZATION
Abstract:
We studied transformation and mineralization of nitrogenous soil polymers by the humivorous larva of the scarabaeid beetle Pachnoda ephippiata, using 14C-labeled peptides, peptidoglycan, and chitin, both native and stabilized by co-polymerization with synthetic humic acids. The results indicated that these materials were solubilized mainly in the alkaline midgut. The solubilization rate of peptides to TCA-soluble products was higher than those of peptidoglycan and chitin. Solubilization rates were lower when the polymers were stabilized in humic acids. Incubation of soil with midgut fluid released amino acids, which explains the high in vivo concentrations of amino acids observed in the midgut fluid. The large amounts of NH+4 in the fresh fecal pellets indicated that at least 1.7% of the total nitrogen (7% of the acid-hydrolyzable peptides) in the ingested soil was mineralized during gut passage; also the amount of soluble protein and the solubility of humic substances increased. The combined evidence supports the hypothesis that not only microbial biomass but also the nitrogen-rich components of humus are important dietary components for humivorous insects, and that feeding activities of soil macroinvertebrates strongly impact transformation and mineralization of soil organic matter.
