AOBPreview originally published online on March 10, 2005
Annals of Botany 2005 95(6):1025-1032; doi:10.1093/aob/mci111
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Biomass Allocation and Leaf Chemical Defence in Defoliated Seedlings of Quercus serrata with Respect to Carbon–Nitrogen Balance
1 Graduate School of Life Sciences, Tohoku University, Aoba, Sendai 980-8578, Japan and 2 Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa 920-1192, Japan
* For correspondence. E-mail hikosaka{at}mail.tains.tohoku.ac.jp
Received: 12 July 2004 Returned for revision: 5 January 2005 Accepted: 25 January 2005 Published electronically: 10 March 2005
• Background and Aims Both nutrient availability and defoliation affect the carbon–nutrient balance in plants, which in turn influences biomass allocation (e.g. shoot-to-root ratio) and leaf chemical composition (concentration of nitrogen and secondary compounds). In this study it is questioned whether defoliation alters biomass allocation and chemical defence in a similar fashion to the response to nutrient deficiency.
• Methods Current-year seedlings of Quercus serrata were grown with or without removal of all leaves at three levels of nutrient availability.
• Key Results Plant nitrogen concentration (PNC), a measure of the carbon–nutrient balance in the plant, significantly decreased immediately after defoliation because leaves had higher nitrogen concentrations than stems and roots. However, PNC recovered to levels similar to or higher than that of control plants in 3 or 6 weeks after the defoliation. Nitrogen concentration of leaves produced after defoliation was significantly higher than leaf nitrogen concentration of control leaves. Leaf mass per plant mass (leaf mass ratio, LMR) was positively correlated with PNC but the relationship was significantly different between defoliated and control plants. When compared at the same PNC, defoliated plants had a lower LMR. However, the ratio of the leaf to root tissues that were newly produced after defoliation as a function of PNC did not differ between defoliated and control plants. Defoliated plants had a significantly lower concentration of total phenolics and condensed tannins. Across defoliated and control plants, the leaf tannin concentration was negatively correlated with the leaf nitrogen concentration, suggesting that the amount of carbon-based defensive compounds was controlled by the carbon–nutrient balance at the leaf level.
• Conclusions Defoliation alters biomass allocation and chemical defence through the carbon–nutrient balance at the plant and at the leaf level, respectively.
Key words: Carbon–nutrient balance, defoliation, nitrogen concentration, Quercus serrata, secondary compounds, shoot/root ratio, tannins, total phenolics
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