Interactions between peat and sodium acetate, ammonium sulphate urea or wheat straw during incubation studied by 13C and 15N NMR spectroscopy |
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| Authors: | L Benzing-Purdie M V Cheshire B L Williams C I Ratcliffe † J A Ripmeester † B A Goodman ‡ |
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| Institution: | Agriculture Canada, Ottawa, Canada K1A 0C6;Macaulay Land Use Research Institute, Aberdeen AB9 2QJ, UK;Division of Chemistry, National Research Council, Ottawa, Canada KA1 OR6;Scottish Crop Institute, Invergowrie, Dundee DD2 5DA, UK |
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| Abstract: | Transformations of sodium acetate, ammonium sulphate, urea and wheat straw in peat have been studied by determining the distribution of 15N-labelled material, and by 13C and 15N nuclear magnetic resonance spectroscopy (NMR) using cross polarization (CP) and magic-angle spinning (MAS). Samples of an oligotrophic blanket peat were incubated for 6 months at 15°C with 15N ammonium sulphate, 15N urea, 13C15N urea, 15N-labelled wheat straw or 13C sodium acetate. The incubated samples were separated into fractions of >1 mm, 1–0.5 mm, 0.5–0.25 mm, 0.25–0.15 mm, 0.15–0.05 mm, 0.05–0.005 mm and a water-soluble fraction by wet sieving, and were then freeze-dried. The distribution of 15N between the fractions was obtained after isotope-ratio analysis by mass spectrometry, and the 0.5–0.25 mm, 0.05–0.005 mm and water-soluble fractions from the incubations were examined by 13C and 15N NMR. 13C-labelled acetate increased carbohydrate resonances in the 0.05–0.005 mm and soluble material, but an organic acid derived from the substrate was still present 6 months later. Incorporation of 15N from ammonium sulphate into the peat was low, and more than 50% of the added N was detected in the soluble fraction still present as 15NH+4. As carbohydrate and soluble organic matter were detected in the peat, it was concluded that microbial activity and N immobilization were restricted by poor aeration and low pH. Urea, in contrast, interacted with all the fractions examined, with some 15N being incorporated into a range of compounds that included protein, peptides, amides, amino acids and carbamates or lactam derivatives. A small proportion of labelled 15N from wheat straw, orginally present in the > 1 mm and 14.5 mm fractions, had moved into the 0.05–0.005 fraction during incubation and sieving. The 13C spectra suggested that the presence of the straw may have stimulated decomposition of the peat components. |
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