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The role of root-associatedKlebsiella pneumoniae in the nitrogen nutrition ofPoa pratensis andTriticum aestivum as estimated by the method of15N isotope dilution
Authors:Kielo Haahtela  Kirsti Kari
Institution:(1) Department of General Microbiology, University of Helsinki, Mannerheimintie 172, SF-00280 Helsinki 28, Finland
Abstract:Summary The technique of15N isotope dilution was used to verify that nitrogen was fixed and transferred to the plant byKlebsiella pneumoniae strain Pp in association withPoa pratensis orTriticum aestivum. Surface sterilized, sprouting seeds were inoculated withK. pneumoniae and grown in sand in modified Leonard jars. Potassium nitrate enriched with15N was used to provide N concentrations ranging from 10–40 mg Nl–1 nutrient solution. After 10–18 weeks the shoots and roots were analyzed separately for dry matter, N content, total N, and atom %15N excess. The acetylene reduction technique was used to test for the presence of N2-fixing organisms on the roots. The data from15N isotope dilution demonstrated that up to 33.8% of N in the shoots ofP. pratensis and 15.9% in those ofT. aestivum were derived from associative N2 fixation byK. pneumoniae. In most experiments the dry matter yield, N content, and total N yield of the shoots ofP. pratensis were increased byK. pneumoniae inoculation, whereas inoculation had no significant effect on the dry matter yield, N content or total N of the shoots ofT. aestivum.
Keywords:Blue grass  Klebsiella pneumoniae  Poa pratensis  Triticum aestivum  Nitrogen fixation  Nitrogen nutrition  15N isotope dilution  Spring wheat
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