Abstract
Nitrification is a key stage in the nitrogen cycle; it enables the transformation of nitrogen into an oxidized, inorganic state1,2. The availability of nitrates produced by this process often limits primary productivity and is an important determinant in plant community ecology and biodiversity3,4,5,6. Chemoautotrophic prokaryotes are recognized as the main facilitators of this process7, although heterotrophic nitrification by fungi may be significant under certain conditions8. However, there has been neither biochemical nor ecological evidence to support nitrification by photoautotrophic plants. Here we show how certain legumes that accumulate the toxin, 3-nitropropionic acid, generate oxidized inorganic nitrogen in their shoots, which is returned to the soil in their litter. In nitrogen-fixing populations this ‘new’ nitrate and nitrite can be derived from the assimilation of nitrogen gas. Normally, the transformation of elemental nitrogen from the atmosphere into a fixed oxidized form (as nitrate) is represented in the nitrogen cycle as a multiphasic process involving several different organisms. We show how this can occur in a single photoautotrophic organism, representing a previously undescribed feature of this biogeochemical cycle.
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Acknowledgements
We thank R. Williams, D. Knight, R. Jones and K. Flynn for their assistance. M.A.S. thanks the Libyan government for financial support. The following botanic gardens supplied seed: Akureyri, Iceland; Bayreuth, Germany; Bern, Switzerland; Bonn, Germany; Bordeaux, France; Bratislava, Slovakia; Caen, France; Cambridge, UK; Dresden, Germany; Firenze, Italy; Halle, Germany; Hamburg, Germany; Innsbruck, Austria; Jenna, Germany; L'Aquila, Italy; Latte, Italy; Leicester, UK; Leipsig, Germany; Lisbon, Portugal; Oldenburg, Germany; Oxford, UK; Padova, Italy; Rouen, France; Sienna, Italy; Strasbourg, France; and Urbino, Italy.
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Supplementary information
Supplementary Notes
Contains information about the production of 3-nitropropionic acid, nitrate and nitrite by axenic cultures of horseshoe vetch, including a photograph of a seedling growing in sterile culture. (DOC 38 kb)
Supplementary Table 1
The proportions of nitrate and nitrite in fresh leaves, senescing leaves and litter of 3NPA-containing species. (DOC 25 kb)
Supplementary Table 2
The amino acid contents of horseshoe vetch and white clover, in water culture and natural populations. (DOC 21 kb)
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Hipkin, C., Simpson, D., Wainwright, S. et al. Nitrification by plants that also fix nitrogen. Nature 430, 98–101 (2004). https://doi.org/10.1038/nature02635
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DOI: https://doi.org/10.1038/nature02635
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