Molecular‐Scale Characterization of Hot‐Water‐Extractable Organic Matter in Organic Horizons of a Forest Soil

Abstract

Hot-water-extractable organic matter (HWEOM) has been shown to be highly correlated with microbial biomass in forest soils. We conducted elemental and 13 C solid-state nuclear magnetic resonance spectroscopic analyses to assess the composition and structural chemistry of HWEOM and its variations with soil depth within O horizons in a forest site in New Hampshire. The HWEOM fraction exhibited a higher H/C ratio and higher O-alkyl C proportion than the soil from which it was extracted. It also had a 30 to 40% lower C/N ratio than the whole soil. The relative proportion of O-alkyl C in the HWEOM increased with soil depth in the forest fl oor, while alkyl C decreased, contrary to the pattern observed for the whole soil. The spectral and elemental properties of HWEOM present in these acidic Spodosols support the hypothesis that HWEOM is largely a mixture of carbohydrates and proteins. We estimate that while HWEOM includes both labile C fractions and microbial biomass, microbial biomass can account for no more than 40% of the C extracted by hot water.

Effects of calcium treatment on forest floor organic matter composition along an elevation gradient

“…The Oie and Oa horizons for this study were subjected to hot-water extraction, as described in detail in Balaria et al (2009). Hot-water extraction was performed by pooling the five replicates on an equal dry-mass basis.…”

“…The specific hypotheses examined in the study were: (1) SOM and its hot-water extractable fraction are richer in structures related to carbohydrates (Oalkyl C) and lignin (O-aryl C) at higher elevations; (2) wollastonite treatment results in organic matter containing less O-alkyl C than organic matter in the reference watershed. We performed this work for Oie and Oa horizons separately, since the structure of both SOM and HWEOM varies with soil depth (Balaria et al 2009;Balaria et al 2013), as did the inorganic chemical response to wollastonite treatment (Cho et al 2010).…”

Properties of dissolved and total organic matter in throughfall, stemflow and forest floor leachate of central European forests

“…Consequently, solid-state 13 C NMR spectroscopy is widely used for the characterization of a range of organic materials from various natural environments (Baldock et al, 2004). It has been applied to soil OM (Helfrich et al, 2006;Keeler et al, 2006), hot water extracts (Leinweber et al, 1995;Balaria et al, 2009) and DOM in aqueous solutions from aquatic (Schumacher et al, 2006) and terrestrial ecosystems Fröberg et al, 2003;Sanderman et al, 2008). Although the technique has been applied to POM from aquatic systems (McKnight et al, 1997;Lankes et al, 2008), to the best of our knowledge, it has never been applied to POM or TOM in aqueous samples from terrestrial ecosystems such as TF, SF or FF leachates.…”

Biodegradation of dissolved organic carbon in soil extracts and leachates from a temperate forest stand and its relationship to ultraviolet absorbance

“…The hot water extracts had relatively higher concentrations of biodegradable organic C compared with the other soil extracts, with no lag phases at the start of the incubation (Figure 1(c)). This can be explained by the fact that hot water extracts contain substantial amounts of labile and bioavailable C such as carbohydrates [29][30][31]. Hot water extractable C is considered to be one of the most sensitive indicators of soil C availability under different forest sites and management regimes [31][32][33][34].…”

“…This can be explained by the fact that hot water extracts contain substantial amounts of labile and bioavailable C such as carbohydrates [29][30][31]. Hot water extractable C is considered to be one of the most sensitive indicators of soil C availability under different forest sites and management regimes [31][32][33][34]. Chloroform fumigation of soil lyses the cells of soil microorganisms and makes their contents partially extractable by CaCl 2 solution.…”