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| Titel |
Isotopic patterns in caps and stipes in sporocarps reveal patterns of organic nitrogen use by ectomycorrhizal fungi |
| VerfasserIn |
Erik Hobbie, Andrew Ouimette, Janet Chen |
| 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 |
250130753
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| Publikation (Nr.) |
 EGU/EGU2016-11054.pdf |
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| Zusammenfassung |
| Current ecosystem models use inorganic nitrogen as the currency of nitrogen acquisition by
plants. However, many trees may gain access to otherwise unavailable soil resources, such as
soil organic nitrogen, through their symbioses with ectomycorrhizal fungi, and this pathway
of nitrogen acquisition may therefore be important in understanding plant responses to
environmental change. Different functional groups of ectomycorrhizal fungi vary in their
ability to enzymatically access protein and other soil resources. Such fungal parameters as
hyphal hydrophobicity, the presence of rhizomorphs (long-distance transport structures), and
exploration strategies (e.g., short-distance versus long-distance, mat formation) correspond
with how fungi interact with and explore the environment, and the proportions of different
exploration types present will shift along environmental gradients such as nitrogen
availability.
Isotopic differences between caps and stipes may provide a means to test for organic
nitrogen use, since caps and stipes differ in δ13C and δ15N as a result of variable proportions
of protein and other classes of compounds, and protein should differ isotopically among de
novo synthesis, litter sources, and soil sources. Here, we propose that (1) isotopic differences
between caps and stipes could be related to organic nitrogen uptake and to the δ13C
and δ15N values of different pools of soil-derived or de novo-synthesized amino
acids; (2) these isotopic differences will reflect greater acquisition of soil-derived
organic nitrogen by exploration types of greater enzymatic capabilities to degrade
recalcitrant nitrogen forms, specifically long-distance, medium-distance fringe, and
medium-distance mat exploration types. To test these hypotheses, we use a dataset of
isotopic values, %N, and %C in 208 cap/stipe samples collected from Oregon, western
USA.
δ13C differences in caps and stipes in a multiple regression model had an adjusted r2 of
0.292 (p < 0.0001), and were explained best by exploration type (45% of explained
variance), the interaction of exploration type and %Ncap−stipe (20%), the interaction of
exploration type and %Ncap∕stipe (22%), %Ccap−stipe (8%), and %Ncap−stipe (5%). δ15N
differences between caps and stipes in a multiple regression model had an adjusted r2 of
0.486 (p < 0.0001), and were explained best by exploration type (47% of explained
variance), the interaction of exploration type and %Ncap−stipe (26%), the interaction of
exploration type and %Ncap∕stipe (14%), %Ncap∕stipe (11%),and %Ccap−stipe
(2%).
We argue that these differences in the 13C and 15N enrichment of caps relative to stipes
reflect not only shifts in the proportions of protein and carbohydrates, but also differences in
the extent of fluxes and the δ13C and δ15N signatures of soil- and litter-derived organic
nitrogen taken up by these fungi. We also propose equations to quantify this uptake. Organic
nitrogen from litter (lower δ13C and δ15N) may be incorporated by medium-distance mat,
short-distance, and contact exploration types of ectomycorrhizal fungi, whereas long-distance
and medium-distance fringe exploration types appeared to incorporate deeper soil organic
nitrogen. |
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