Long term changes in the distribution and delta N-15 values of individual soil amino acids in the absence of plant and fertiliser inputs

Bol, Roland; Ostle, Nick J.; Chenu, Claire C.; Petzke, Klaus-Jurgen; Werner, Roland A.; Balesdent, Jerome. 2004 Long term changes in the distribution and delta N-15 values of individual soil amino acids in the absence of plant and fertiliser inputs. Isotopes in Environmental and Health Studies, 40 (4). 243-256.

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The long-term 'biodegradation' on soil amino acids was examined in the control plots of '42 parcelles' experiment, established in 1928 at INRA, Versailles (France). None of the plots is cultivated, but is kept free of weeds, and mixed to a depth of 25 cm twice yearly. Topsoil (0-10 cm depth) samples collected in 1929, 1963 and 1997 were subjected to acid hydrolysis (6 N HCl) for comparison. The distribution and δ15N natural abundance of 20 individual amino acids in the soils were determined, using ion chromatography (IC) and gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). The total N and amino acid-N (AA-N), respectively, decreased by 54 % and 73 % in the period from 1929 to 1997. The average N loss was comparable for 1929-1963 (period 1) and 1963-1997 (period 2), but AA-N loss was three times faster in the former period. This significant reduction in total AA-N content was mirrored in the individual amino acids, which decreased by 74 % ± 1 % (ranging 58-89 %) between 1929 and 1997. The bulk δ15N values generally increased from 1929 to 1997, mainly associated with comparable or even higher increase of δ15N of the non-AA-N in the soil. The residence time (t1/2, time in which half of N was lost from a specific soil pool) was ca. 65 ± 5 years for the bulk soil, and comparable for periods 1 and 2. However, between periods 1 and 2 it decreased from 128 to 41 years in the non-AA pool, but increased from 59 to 92 years in the AA-N pool. Proline and amino acids that appear early in soil microbial metabolic pathways (e.g. glutamic acid, alanine, aspartic acid and valine) had relatively high δ15N values. Phenylalanine, threonine, glycine and leucine had relatively depleted δ15N values. The average δ15N value of the individual amino acids (IAAs) increased by 1δ unit from 1929 to 1997, associated with a similar rise from 1929 to 1963, and no change thereafter till 1997. However, the δ15N values of phenylalanine decreased by more than 7δ15N units between 1929 and 1997. The δ15N shift of IAAs from 1929 to 1963 and from 1929 to 1997 was not influenced by the relative amount of N remaining compared with the 1929 soil concentrations. The only exception was phenylalanine which showed decreasing δ15N associated with its decreasing concentration in the soil. We conclude therefore that in the absence of plant and fertiliser inputs, no change in the δ15N value of individual soil amino acids occurs, hence the original δ15N values are preserved and diagnostic information on past soil N (cycling) is retained. The exception was phenylalanine, its δ15N decreased with decreasing concentration from 1929 to 1997, hence it acted as a 'potential' marker for the land use changes (i.e. arable cropping to a fallow). The long term biological processing and reworking of residual amino acids resulted in a (partial) stabilisation in the soil, evidenced by reduced N loss and increased residence time of amino acid N during the period 1963-1997.

Item Type: Publication - Article
Digital Object Identifier (DOI):
Programmes: CEH Programmes pre-2009 publications > Biogeochemistry > BG01 Measuring and modelling trace gas, aerosol and carbon > BG01.2 Carbon
UKCEH and CEH Sections/Science Areas: Shore
ISSN: 1025-6016
Additional Information. Not used in RCUK Gateway to Research.: Revised version of the Isotopenpreis winner's contribution to the 26th Annual Meeting of the German Association for Stable Isotope Research (GASIR) October, 6–8, 2003, Cologne, Germany
Additional Keywords: Amino acids, Fertiliser, GC-C-IRMS, Natural variations, Nitrogen-15, Phenylalanine, Plant, Protein, Soil
NORA Subject Terms: Agriculture and Soil Science
Biology and Microbiology
Ecology and Environment
Earth Sciences
Date made live: 01 Sep 2009 14:24 +0 (UTC)

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