Compound‐specific δ¹³C analysis of individual amino sugars – a tool to quantify timing and amount of soil microbial residue stabilization

Abstract

There is strong scientific evidence that microbial residues such as amino sugars may be stabilized in soil. However, up to now, no investigation has been carried out to quantify both the amount and timing of such stabilization. This is primarily due to methodological constraints, because it is not possible to differentiate between stabilized (old) and recently produced (new) amino sugars when these biomarkers are conventionally analyzed, e.g. by means of gas chromatography and flame ionization detection. Therefore, the aim of the present study was to test whether compound-specific isotope analysis (delta13C) of amino sugars extracted from soil could be used to differentiate between old and new microbial residues. For this aim a method for the delta13C analysis of individual amino sugars was developed and optimized. First results of delta13C values of glucosamine, galactosamine, mannosamine, and muramic acid in soil samples from two different ecological studies are presented, clearly indicating that discrimination between soil inherent and newly formed amino sugars is possible in stable isotope labeling experiments. Our results further showed that, in the short term (within 1 month), only few amino sugars were built, thus making highly 13C-enriched substrates necessary for the quantification of new amino sugar production and for the determination of amino sugar turnover rates.

Soil redistribution and weathering controlling the fate of geochemical and physical carbon stabilization mechanisms in soils of an eroding landscape

“…For example, the abundance of amino sugars (AS) and the 14 C derived age of a fraction can indicate the potential of a specific mechanism to protect SOC against further degradation. The large majority (> 99 %) of AS found in soils are considered to be of microbial origin and constitute an important building block in cell walls and extracellular polysaccharides (Glaser et al, 2004;Glaser and Gross, 2005;Simpson, 2004). In soils, only glucosamine (GluN), galactosamine (GalN), and muramic acid are found in quantifiable concentrations.…”

Optimizing sample pretreatment for compound-specific stable carbon isotopic analysis of amino sugars in marine sediment

“…The latter technique has been widely employed in soil science to investigate the formation and/or turnover kinetics of amino sugars (e.g., Glaser et al, 2005;Decock et al, 2009;Bai et al, 2012). However, to date, the isotopic composition of amino sugars in marine sediment remains poorly explored, partly because of the much lower concentration of amino sugars in marine sediment compared to soil, which results in the need for an efficient pretreatment procedure to enable precise isotopic determination.…”

“…Compound-specific δ 13 C analysis of amino sugars is commonly performed via isotope ratio mass spectrometry (IRMS) after separation of compounds by either gas chromatography (GC; Glaser and Gross, 2005), liquid chromatography (LC; or, more recently, ion chromatography (IC; Dippold et al, 2014). Compared with LC-IRMS, the GC-based method is less sensitive to adverse effects of the sample matrix on detection (McCullagh, 2010;Morrison et al, 2010;Rinne et al, 2012), and requires smaller amounts of amino sugars.…”

“…Compared with LC-IRMS, the GC-based method is less sensitive to adverse effects of the sample matrix on detection (McCullagh, 2010;Morrison et al, 2010;Rinne et al, 2012), and requires smaller amounts of amino sugars. The accuracy and precision of the GC-based method, though compromised by the introduction of carbon during derivatization (Glaser and Gross, 2005), has been shown to sufficiently resolve molecular isotopic differences caused by diverse biogeochemical processes in marine sediments (cf. Lin et al, 2010).…”

“…The ANA method produced the most stable derivatives and satisfying results (see below); the corresponding GC operation conditions were specified here in detail. Separation of ANA derivatives in the Optima 17MS column was modified from Glaser and Gross (2005). The injector temperature was 250 • C, and helium was used as a carrier gas at a constant flow rate of 1 ml min −1 .…”