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| Titel |
Organic N cycling revealed through 15N,13C-stable isotope probing of the soil amino acid metabolome |
| VerfasserIn |
Timothy Knowles, David Chadwick, Roland Bol, Richard Evershed |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250052524
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| Zusammenfassung |
| The availability of biologically accessible forms of N influences the diversity, dynamics
and functioning of many ecosystems including soils. Although the cycling and
interconversions between inorganic forms of N in soils are relatively well constrained,
much less is currently known about the fate of organic N-containing compounds.
Organic N represents the vast majority of natural N inputs to soils and of these,
proteins, peptides and amino acids are the most significant. Determining the rates and
pathways of N and C flux from such sources is vital to gain a detailed understanding of
natural (and perturbed system) N cycling. Herein we adopted a compound-specific
dual-stable isotope probing approach to trace N and C within the soil amino acid
metabolome.
A grassland soil was incubated with dual 15N,13C-labelled substrates (glutamate, glycine
and cow dung) in separate incubations, enabling the fate of their N and C to be followed over
a time course (between 3 h and 32Â d). A molecular level approach was adopted throughout,
whereby chemically and isotopically defined substrates were added to soil before isotopic
analyses of individual soil amino acids, respired CO2 and bulk soil. Compound-specific N
and C isotope analyses of soil amino acids, following addition of individual amino acid
substrates, revealed highly conservative biochemical processing by the soil microbial
community, such that the biochemical behaviour of a whole soil reflects that of an individual
microorganism; highlighting the conservative nature of primary cellular metabolism
even at a systems level. The mass balance approach adopted throughout and the
application of linear and non linear regressions enabled rate constants and fluxes of
15N and 13C label into de novo biosynthesised amino acids to be determined in
addition to measures of the ‘biochemical proximity’ of substrates and products. Such
information is vital to the creation of models of soil N dynamics whose structure is
based in fundamental cellular biochemistry, which would potentially demonstrate a
wider applicability to a large range of systems. Significant decoupling of the soil
N and C cycles was demonstrated at the amino acid level, whereby the disparate
fates of C and N from substrates in which they were covalently linked are clearly
apparent.
This approach was extended to investigations into the physical transport and biochemical
transformations of dung-derived N and C shortly after its addition to soil. These experiments
revealed valuable information regarding the transport processes involved in dung N and C
incorporation into soil, and the chemical forms in which it is transported. The application of
these techniques to studies of metabolic processes is not limited to soils and sediments;
valuable information regarding C and N metabolism in other ecosystems and, indeed,
individual species of micro- and macro- organisms could be derived in this way. |
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