Response of small birch plants (Betula pendula Roth.) to elevated CO2 and nitrogen supply

Authors

  • R. PETTERSSON,

    Corresponding author
    1. Department of Ecology and Environmental Research, Swedish University of Agricultural Sciences, P.O. Box 7072, S-750 07 Uppsala, Sweden
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  • A. J. S. McDONALD,

    1. Department of Ecology and Environmental Research, Swedish University of Agricultural Sciences, P.O. Box 7072, S-750 07 Uppsala, Sweden
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  • I. STADENBERG

    1. Department of Ecology and Environmental Research, Swedish University of Agricultural Sciences, P.O. Box 7072, S-750 07 Uppsala, Sweden
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  • The authors wish to thank Elisabeth Arwidsson and Annette Hovberg for growing the plants, and Anita Flower-Ellis for analysis of carbohydrates. We also wish to thank Professor Sune Linder for his comments on the manuscript and helpful support throughout. Professor Göran Ågren and Dr Helen Lee made valuable comments on the draft manuscript. The research was funded by grants from the Swedish Council for Forestry and Agricultural Research.

Roger Pettersson, Department of Ecology and Environmental Research, Swedish University of Agricultural Sciences, P.O. Box 7072, S-75007 Uppsala, Sweden.

ABSTRACT

Small birch plants were grown for up to 80 d in a climate chamber at varied relative addition rates of nitrogen in culture solution, and at ambient (350 μmol mol-1) or elevated (700 μmol mol-1) concentrations of CO2. The relative addition rate of nitrogen controlled relative growth rate accurately and independently of CO2 concentration at sub-optimum levels. During free access to nutrients, relative growth rate was higher at elevated CO2. Higher values of relative growth rate and net assimilation rate were associated with higher values of plant N-concentration. At all N-supply rates, elevated CO2 resulted in higher values of net assimilation rate, whereas leaf weight ratio was independent of CO2. Specific leaf area (and leaf area ratio) was less at higher CO2 and at lower rates of N-supply. Lower values of specific leaf area were partly because of starch accumulation. Nitrogen productivity (growth rate per unit plant nitrogen) was higher at elevated CO2. At sub-optimal N-supply, the higher net assimilation rate at elevated CO2 was offset by a lower leaf area ratio. Carbon dioxide did not affect root/shoot ratio, but a higher fraction of plant dry weight was found in roots at lower N-supply. In the treatment with lowest N-supply, five times as much root length was produced per amount of plant nitrogen in comparison with optimum plants. The specific fine root length at all N-supplies was greater at elevated CO2. These responses of the root system to lower N-supply and elevated CO2 may have a considerable bearing on the acquisition of nutrients in depleted soils at elevated CO2. The advantage of maintaining steady-state nutrition in small plants while investigating the effects of elevated CO2 on growth is emphasized.

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