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| Titel |
The effect of local ectomycorrhizal nitrogen supply on allocation of recent photosynthates within the mycorrhizosphere |
| VerfasserIn |
Stefan Gorka, Werner Mayerhofer, Marlies Dietrich, Raphael Gabriel, Julia Wiesenbauer, Victoria Martin, Peter Schweiger, Dagmar Woebken, Andreas Richter, Christina Kaiser |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250151348
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| Publikation (Nr.) |
 EGU/EGU2017-15917.pdf |
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| Zusammenfassung |
| Understanding allocation patterns of carbon (C) released by plants into their soil environment
is vital for understanding global C cycling. Plants release photosynthetically acquired
C not only to the rhizosphere and respective soil bacteria, but also to associated
mycorrhizal fungi. Mycorrhizal fungi extend further into the adjacent soil, mining for
essential nutrients like nitrogen (N) and phosphorous (P), with a dramatically increased
surface area compared to plant roots. Symbiotically, plants receive these nutrients in
exchange for C. A reciprocal control on exchange rates has been shown in arbuscular
mycorrhizal systems, but the situation remains equivocal for the ectomycorrhizal (EM)
symbiosis. Furthermore, the symbiosis may conceptually be extended to interactions
between mycorrhizal fungal hyphae and soil bacteria. For example, a transfer of
plant-derived C from hyphae to surrounding soil microbial communities has been
suggested, with however only limited experimental evidence. We hypothesized
that (i) reciprocal reward within the EM symbiosis may be observed at the level of
root system architecture, i.e. that plants allocate C preferentially to parts of their
root system that receive more N by EM fungi, (ii) that EM fungi allocate recent
photosynthates to soil bacteria, and (iii) that this C allocation is influenced by N
availability.
We conducted a split-root experiment with ectomycorrhizal beech (Fagus sylvatica) trees.
Young trees were collected in the Wienerwald near Vienna. Each plant was transferred to a
‘split-root’-box, dividing its root system into two parts, with each part growing into one
of two disconnected soil compartments. Each of the two soil compartments was
connected to a separated litter compartment by a mesh (35 μm) penetrable only for
fungal hyphae, but not for roots. Stable isotope tracing was used for determining
the fate of nutrients and photosynthates in this system, by applying 15N labelled
ammonium and amino acids to only one of the two litter compartments, while exposing
aboveground plants to a 13CO2 enriched atmosphere. Subsequently, we used EA-IRMS
to trace isotopic signals in bulk components, and GC-MS/GC-IRMS for PLFA
quantification.
Our results show a rapid transport of 15N to plants via EM hyphae, and photosynthetically
fixed 13C toward hyphal tips, with already significant enrichments 17 hours after 13CO2
labelling and 40 hours after 15N addition. No plant control for reciprocal C-N exchange at the
bulk root scale was found. We argue that investigations at smaller scales are required, as
regression analysis shows a trend towards reciprocal exchange (R2 = 0.32, p < 0.001) when
separating roots into branches. Furthermore, we found significant enrichment of 13C in
bacteria-specific PLFAs in the hyphae-exclusive litter compartment. This indicates a rapid
allocation of recent photosynthates to remote soil bacteria through EM hyphae. |
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