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| Titel |
Assessing microbial utilization of free versus sorbed Alanine by using position-specific 13C labeling and 13C-PLFA analysis |
| VerfasserIn |
Jennifer Herschbach, Carolin Apostel, Sandra Spielvogel, Yakov Kuzyakov, Michaela Dippold |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250133809
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| Publikation (Nr.) |
 EGU/EGU2016-14461.pdf |
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| Zusammenfassung |
| Microbial utilization is a key transformation process of soil organic matter (SOM). Sorption
of low molecular weight organic substances (LMWOS) to soil mineral surfaces blocks or
delays microbial uptake and therefore mineralization of LMWOS to CO2, as well as all other
biochemical transformations. We used position-specific labeling, a tool of isotope
applications novel to soil science, combined with 13C-phospholipid fatty acid (PLFA)
analysis, to assess microbial utilization of sorbed and non-sorbed Alanine in soil. Alanine has
various functional groups enabling different sorption mechanisms via its positive charge (e.g.
to clay minerals by cation exchange), as well as via its negative charge (e.g. to iron oxides by
ligand exchange).
To assess changes in the transformation pathways caused by sorption, we added
uniformly and position-specifically 13C and 14C labeled Alanine to the Ap of a loamy
Luvisol in a short-term (10 days) incubation experiment. To allow for sorption of the tracer
solution to an aliquot of this soil, microbial activity was minimized in this subsample
by sterilizing the soil by γ-radiation. After shaking, the remaining solutions were
filtered and the non-sorbed Alanine was removed with Millipore water and then
added to non-sterilized soil. For the free Alanine treatment, solutions with Alanine
of similar amount and isotopic composition were prepared, added to the soil and
incubated as well. The respired CO2 was trapped in NaOH and its 14C-activity was
determined at increasing times intervals. Microbial utilization of Alanine’s individual
C positions was evaluated in distinct microbial groups classified by 13C-PLFA
analysis.
Sorption to soil minerals delayed respiration to CO2 and reduced initial respiration rate by
80%. Irrespective of sorption, the highest amount was respired from the carboxylic
position (C-1), whereas the amino-bound (C-2) and the methylic position (C-3)
were preferentially incorporated into PLFA of microorganisms due to the basic
microbial metabolism of C3 molecules in glycolysis. Reconstruction of microbial
transformation pathways showed that the C-2 position of Alanine was lost as CO2
faster than its C-3 position regardless of whether the molecule was used ana- or
catabolically. The highest incorporations of all positions in PLFA were accomplished
by Gram negatives. Free Alanine was preferentially used by highly competitive
prokaryotes, while sorbed Alanine was preferred by filamentous microorganisms.
In detail, the free living osmotrophic Gram negative bacteria utilize more easily
accessible dissolved substances. The utilization of sorbed substances are achieved by
less mobile microorganisms, e.g. eukaryotic fungi and Actinomycetes, which form
biofilms.
None of these findings could have been achieved without the position-specific labeling
approach, therefore this method will strongly improve our understanding of stabilization
processes and soil C fluxes. |
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