Environmental Chemistry Environmental Chemistry Society
Environmental problems - Chemical approaches
RESEARCH ARTICLE

Comparison of nuclear magnetic resonance methods for the analysis of organic matter composition from soil density and particle fractions

Joyce S. Clemente A , Edward G. Gregorich B , André J. Simpson A , Rajeev Kumar C , Denis Courtier-Murias A and Myrna J. Simpson A D

A Department of Chemistry, University of Toronto, 1265 Military Trail, Toronto, ON, M1C 1A4, Canada.

B Agriculture and Agri-food Canada, Central Experimental Farm, Ottawa, ON, K1A 0C6, Canada.

C Bruker BioSpin Ltd., 555 Steeles Avenue East, Milton, ON, L9T 1Y6, Canada.

D Corresponding author. Email: myrna.simpson@utoronto.ca

Environmental Chemistry 9(1) 97-107 http://dx.doi.org/10.1071/EN11096
Submitted: 21 July 2011  Accepted: 19 December 2011   Published: 23 February 2012

Environmental context. The association of specific organic matter (OM) compounds with clay mineral surfaces is believed to protect these compounds from degradation and thus result in long-term protection in soil. The molecular-level composition of soil OM associated with soil fractions was measured and compared using solid-state 13C nuclear magnetic resonance (NMR) and solution-state 1H NMR methods. Combining these methods allowed more detailed characterisation of OM associated with different soil fractions and will improve the understanding of OM dynamics in soil.

Abstract. Organic matter (OM) associated with fine soil fractions is hypothesised to be protected from complete biodegradation by soil microbes. It is therefore important to understand the structure and stage of decomposition of OM associated with various soil fractions. Solid-state 13C nuclear magnetic resonance (NMR) spectroscopy has been used extensively to investigate the OM composition of soils and soil fractions. Solution-state 1H NMR spectroscopy has not been used as much but is an emerging tool for analysing soil OM because 1H NMR spectra are often better resolved and provide information that complements the structural information obtained from solid-state 13C NMR experiments. This study compares one-dimensional solution-state 1H NMR and solid-state 13C NMR methods for assessing the degradation and composition of OM in three different soils, and their light and clay-size fractions. The alkyl/O-alkyl degradation parameter was consistent across all NMR methods and showed that OM associated with clay-size fractions were at more advanced stages of degradation as compared to that in light density soil fractions. Solution-state 1H and diffusion edited (DE) 1H NMR results showed the presence of high concentrations of microbial-derived peptidoglycan and peptide side-chains in clay-sized fractions. Lignin was also identified in clay-sized fractions using solid-state 13C and solution-state 1H NMR techniques. The combination of solid-state 13C and solution-state 1H NMR methods provides a more detailed analysis of OM composition and thereby facilitates a better understanding of the fate and preservation of OM in soil.

Additional keywords: clay-size fraction, light density fraction, microbial-derived organic matter, plant-derived organic matter, solid-state 13C NMR, solution-state 1H NMR.


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