Differentiating the dynamics of native and newly immobilized amino sugars in soil frequently amended with inorganic nitrogen and glucose

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The application of available substrates regulates the soil‐microbial environment and thus directly affects microbial metabolic processes. As stable microbial residues, the turnover of soil amino sugars is dependent on the availability of fresh inputs of carbon and nitrogen (N), which can be investigated by differentiating between the newly synthesized and the natively resistant fractions by isotope tracing techniques. Therefore, a series of incubations were conducted with soils amended with glucose plus 15 N‐labelled inorganic N. The treatments included (i) glucose + 15 NH 4 + added once a week, (ii) glucose + 15 NO 3 − added once a week and (iii) glucose added once a week, but 15 NH 4 + added every 3 weeks. The 15 N enrichment in the target compound was identified by gas chromatography/mass spectrometry (GC/MS) and the dynamics of amino sugars were found to be compound‐specific in response to different substrate applications. The content of 15 N‐containing glucosamine increased significantly across all treatments but the unlabelled portion was decreased only after glucose + 15 NO 3 − amendment. The synthesis of 15 N‐labelled muramic acid was concomitant with the decomposition of the original unlabelled soil portion and the net accumulation occurred in the glucose + 15 NH 4 + treatment. Both the increase and decline of galactosamine content was smaller and showed no significant difference among treatments. Using the dynamics of glucosamine and muramic acid as a basis, the response of different microbial communities to glucose and nitrogen additions was observed. Fungal cell wall residues mainly contributed to the stabilization of soil organic matter, while bacterial cell wall components were easily degraded to provide either carbon or N.