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| Titel |
Compound-specific 15N analysis of amino acids in 15N tracer experiments provide an estimate of newly synthesised soil protein from inorganic and organic substrates |
| VerfasserIn |
Alice Charteris, Katerina Michaelides, Richard Evershed |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250113292
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| Publikation (Nr.) |
 EGU/EGU2015-13607.pdf |
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| Zusammenfassung |
| Organic N concentrations far exceed those of inorganic N in most soils and despite much
investigation, the composition and cycling of this complex pool of SOM remains poorly
understood. A particular problem has been separating more recalcitrant soil organic N
from that actively cycling through the soil system; an important consideration in N
cycling studies and for the soil’s nutrient supplying capacity. The use of 15N-labelled
substrates as stable isotope tracers has contributed much to our understanding of the soil
system, but the complexity and heterogeneity of soil organic N prevents thorough
compound-specific 15N analyses of organic N compounds and makes it difficult to examine
any 15N-labelled organic products in any detail. As a result, a significant proportion
of previous work has either simply assumed that since the majority of soil N is
organic, all of the 15N retained in the soil is organic N (e.g. Sebilo et al., 2013) or
subtracted 15N-labelled inorganic compounds from bulk values (e.g. Pilbeam et al.,
1997). While the latter approach is more accurate, these methods only provide an
estimate of the bulk 15N value of an extremely complex and non-uniformly labelled
organic pool. A more detailed approach has been to use microbial biomass extraction
(Brookes et al., 1985) and subsequent N isotopic analysis to determine the 15N value of
biomass-N, representing the fraction of 15N assimilated by microbes or the 15N cycling
through the ‘living’ or ‘active’ portion of soil organic N. However, this extraction
method can only generate estimates and some lack of confidence in its validity and
reliability remains. Here, we present an alternative technique to obtain a measure
of the assimilation of an applied 15N substrate by the soil microbial biomass and
an estimate of the newly synthesized soil protein, which is representative of the
magnitude of the active soil microbial biomass. The technique uses a stable isotope
tracer and compound-specific 15N analysis, but unlike previous works analyses for
amino acids (representing organic products) rather than ammonium (NH4+) and
nitrate (NO3-). Amino acids are commonly referred to as ‘the building blocks of
life’ as they form the proteins which regulate life’s essential biochemical reactions.
Proteinaceous matter generally comprises 20-40% of total soil N and is ubiquitous in
living organisms, so is a likely ‘organic product’ of microbial activity/assimilation.
Hence, we consider it likely that amino acids represent the major organic nitrogenous
products and a reasonable ‘proxy’ for/measure of the assimilation of an applied 15N
substrate by the soil microbial biomass and an estimate of the newly synthesized soil
protein.
Brookes, P. C. et al. Soil Biol Biochem. 1985, 17, 837-842.
Jenkinson, D. S. et al. Soil Biol Biochem. 2004, 36, 5-7.
Nannipieri, P. et al. Plant Soil. 1999, 208, 43-56.
Pilbeam, C. J. et al. J Agr Sci. 1997, 128, 415-424.
Sebilo, M. et al. PNAS. 2013, 110, 18185-18189. |
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