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The role of N efflux and root abscission in determining plant δ 15 N

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Abstract

Aims

We investigated the relationship between plant δ15N and rates of nitrate supply in wheat (Triticum aestivum; L. cv. SST015) and how this relates to N efflux and root abscission.

Methods

Wheat was grown in sand with NO3 − supplied at five relative addition rates (RAR). We periodically determined the δ15N of roots and shoots as well as the N accumulation in the growth medium due to efflux and root abscission.

Results

Plant δ15N values decreased when N supply exceeded plant demand; e.g. after 47 d plant δ15N of RAR 0.075 d−1 was 0.4‰ but was −4.1‰ at RAR 0.175 d−1. 23% of N taken up would need to be effluxed in order to explain the plant δ15N value of RAR 0.175 d−1. By contrast, the loss of only 2.3% of root biomass could explain this plant δ15N. Indeed, four-fold more N was lost from plants across all RAR’s than accumulated in the growth medium leachate. This excess N loss was likely due to root abscission.

Conclusions

Plant δ15N is influenced by a combination of efflux and root abscission but the proportion of each changes as N supply increases. The efflux of 15N–enriched inorganic N is more likely at high N supply, whereas with lower N supply plants probably lose more N in root fragments.

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Acknowledgements

We would like to thank Ian Newton (Department of Archeometry, UCT) for conducting the mass spectrometer analysis. We are grateful to Bouwer Rall at Wesgraan (Kaap Agri) for providing the wheat seed and to Simon Power for comments that improved the manuscript. Funding for this research was provided by the National Research Foundation (NRF), South Africa.

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Authors and Affiliations

  1. Department of Biological Sciences, University of Cape Town, Private Bag X3, Rondebosch, 7701, South Africa

    Kirsten F. Packer & Michael D. Cramer

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  1. Kirsten F. Packer
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  2. Michael D. Cramer
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Correspondence to Kirsten F. Packer.

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Responsible Editor: Ad C. Borstlap.

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Packer, K.F., Cramer, M.D. The role of N efflux and root abscission in determining plant δ 15 N . Plant Soil 416, 551–563 (2017). https://doi.org/10.1007/s11104-017-3237-6

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