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Doctoral thesis, 2015

Soil nitrogen fluxes and root uptake in the boreal forest : key processes to plant nitrogen nutrition

Oyewole, Olusegun Ayodeji

Abstract

Nitrogen (N) is essential for growth and net primary production of plants. However, N acquisition by plants is influenced by movement of soil N compounds from bulk soil to plant roots and uptake of N by roots. This thesis is aimed at deepening our knowledge on these key processes involved in plant N acquisition in the N-limited boreal forest. To address this aim, a novel, non-invasive microdialysis technique was employed. Amino acids dominated N fluxes in the boreal forest soils. Further, plant roots were shown to have the capacity to absorb organic and inorganic N present in the measured soil fluxes, but these soil fluxes, rather than root uptake, may limit plant N acquisition. The microdialysis technique was further developed to enable simultaneous estimation of diffusion and mass flow of N in soil. Applying this refinement of the technique in the field showed that mass flow significantly increased flux rates of soil N in the boreal forest ecosystem, and that it also altered the chemical composition of the N fluxes. The results from the studies presented in this thesis highlight the potential of the microdialysis technique to improve our understanding of the intrinsic processes involved in N acquisition by plant roots. They also suggest that amino acids might comprise an important source of N for plants in the boreal forest ecosystem. The results suggest that mass flow plays an important role for plant N acquisition in the boreal forest, and mass flow might increase the share of nitrate, particularly in nutrient-rich ecosystems. This finding opens a discussion on the role of transpiration in plant N nutrition, with implications for our understanding of how plant N nutrition will be affected by, among other things, elevated CO2, increased temperatures, and N fertilization.

Keywords

amino acids; diffusion; mass flow; microdialysis; nitrogen availability; nitrogen uptake; plant nutrition; stable isotopes; transpiration

Published in

Acta Universitatis Agriculturae Sueciae
2015, number: 2015:126
ISBN: 978-91-576-8450-9, eISBN: 978-91-576-8451-6
Publisher: Department of Forest Ecology and Management, Swedish University of Agricultural Sciences

    Associated SLU-program

    Future Agriculture (until Jan 2017)
    Future Forests (until Jan 2017)
    Acidification
    Climate
    Eutrophication
    Forest
    SLU Future Forests

    UKÄ Subject classification

    Soil Science
    Forest Science
    Agricultural Science

    Permanent link to this page (URI)

    https://res.slu.se/id/publ/68888