A Molecular Budget for a Peatland Based Upon ¹³C Solid‐State Nuclear Magnetic Resonance

Abstract

Peatlands can accumulate organic matter into long‐term carbon (C) storage within the soil profile. This study used solid‐state 13C nuclear magnetic resonance (13C‐NMR) to investigate the transit of organic C through a peatland ecosystem to understand the molecular budget that accompanies the long‐term accumulation of C. Samples of biomass, litter, peat soil profile, particulate organic matter, and dissolved organic matter (DOM) were taken from the Moor House National Nature Reserve, a peat‐covered catchment in northern England where both the dry matter and C budget for the ecosystem were known. The results showed that: The interpretation of the 13C‐NMR spectra shows that polysaccharides are preferentially removed through the ecosystem, while lignin components are preferentially retained and come to dominate the organic matter accumulated at depth in the profile. The DOM is derived from the oxidation of both biomass and the degradation of lignin, while the particulate organic matter is derived from erosion of the peat profile. The DOM is differentiated by its proportion of oxidized functional groups and not by its aromatic content. The changes in functionality leading to DOM production suggest side chain oxidation resulting in C‐C cleavage/depolymerisation of lignin, a common reaction within white rot fungi. The 13C‐NMR budget shows that O‐alkyl functional groups are disproportionately lost between primary production and accumulation in the deep peat, while C‐alkyl functional groups are disproportionately preserved. The carbon lost as gases (CO2 and CH4) was estimated to be composed of 93% polysaccharide‐derived carbon and 7% lignin‐derived carbon.

Limited Influence of Nutrient Additions to the Transformation of Dissolved and Particulate Organic Matter From a Peatland Headwater

“…The C:N ratios found in this study (between 9 and 23) are similar to those found in other studies of peat‐derived DOM and POM, but much lower than those of peat, or of the vegetation found on the peat (25–29 (DOM and POM), median of 52 (peat), and 37 to 58 (vegetation); Armstrong et al., 2015; Clay & Worrall, 2015; Moody et al., 2018). The values are generally higher than those of mineral soils (12.6; Clay & Worrall, 2015), or POM from various UK rivers (9.2–14.3; Worrall, Burt, & Howden, 2016).…”

“…Solid‐state 13 C‐NMR spectra were recorded at 100.56 MHz using a Varian VNMRS spectrometer and a 4 mm magic‐angle spinning probe at the EPSRC UK National Solid‐state NMR Service at Durham University, using the same method as Moody et al. (2018). The maximum peak height in each eight chemical shift ranges (0–45 ppm C‐alkyl; 45–65 ppm N‐alkyl and methoxyl‐C; 65–95 ppm O‐alkyl‐C; 95–110 ppm O 2 ‐alkyl‐C; 110–145 aromatic/unsaturated C; 145–160 ppm phenolic C; 160–190 ppm carboxyl/amide C; 190–220 ppm aldehyde/ketone C; Baldock & Skjemstad,and Skjemstad, 2000; Hockaday et al., 2009) was divided by the percentage carbon content (from the elemental analysis) to get a relative peak height for each functional group type of carbon observed.…”

“…These provided a background concentration of 15 N in the DOM samples.The 13 C solid-state NMR was used to identify the main functional groups of the DOM samples. Solid-state 13 C-NMR spectra were recorded at 100.56 MHz using a Varian VNMRS spectrometer and a 4 mm magic-angle spinning probe at the EPSRC UK National Solid-state NMR Service at Durham University, using the same method asMoody et al (2018). The maximum peak height in each eight chemical shift ranges (0-45 ppm C-alkyl; 45-65 ppm N-alkyl and methoxyl-C; 65-95 ppm O-alkyl-C; 95-110 ppm O2-alkyl-C; 110-145 aromatic/unsaturated C; 145-160 ppm phenolic C; 160-190 ppm carboxyl/amide C; 190-220 ppm aldehyde/ketone C; Baldock and Skjemstad 2000; Hockaday et al 2009)…”

Characterization of elemental ratios and oxidative ratio of horticultural peat

“…Recent work in a United Kingdom blanket bog utilizing the C ox /OR approach along with other analytical techniques (e.g. 13 C‐NMR) shows that polysaccharides are preferentially removed through decomposition leaving behind more lignin‐like compounds in the residual peat (Moody et al., 2018; Worrall et al., 2016).…”

Thermodynamic Control of the Carbon Budget of a Peatland

“…More recently. Moody et al () have used solid state 13 C‐NMR to give a molecular budget for a peatland and so show that alkyl functional groups were selectively retained.…”