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| Titel |
A reduced fraction of plant N derived from atmospheric N (%Ndfa) and reduced rhizobial nifH gene numbers indicate a lower capacity for nitrogen fixation in nodules of white clover exposed to long-term CO2 enrichment |
| VerfasserIn |
T. Watanabe, S. Bowatte, P. C. D. Newton |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 10, no. 12 ; Nr. 10, no. 12 (2013-12-16), S.8269-8281 |
| Datensatznummer |
250085480
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| Publikation (Nr.) |
 copernicus.org/bg-10-8269-2013.pdf |
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| Zusammenfassung |
| Using the δ15N natural abundance method, we found that the fraction of
nitrogen derived from atmospheric N (%Ndfa) in field-grown white clover
(Trifolium repens L.) plants was significantly lower (72.0% vs.
89.8%, p = 0.047 in a grassland exposed to elevated CO2 for 13 yr
using free air carbon dioxide enrichment (FACE). Twelve months later we
conducted an experiment to investigate the reasons behind the reduced N
fixation. We took cuttings from white clover plants growing in the FACE and
established individual plants in a glasshouse using soil from the appropriate
ambient or elevated CO2 treatments. The established plants were then
transplanted back into their "rings of origin" and sampled over a 6-week
period. We used molecular ecological analyses targeting nifH genes and
transcripts of rhizobia in symbiosis with white clover (Trifolium
repens L.) to understand the potential mechanisms. Shoot biomass was
significantly lower in eCO2, but there was no difference in nodule number
or mass per plant. The numbers of nifH genes and gene transcripts per nodule
were significantly reduced under eCO2, but the ratio of gene to
transcript number and the strains of rhizobia present were the same in both
treatments.
We conclude that the capacity for biological nitrogen fixation was reduced by
eCO2 in white clover and was related to the reduced rhizobia numbers in
nodules. We discuss the finding of reduced gene number in relation to factors
controlling bacteroid DNA amount, which may imply an influence of nitrogen as
well as phosphorus. |
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