Correlation between relative growth rate and specific leaf area requires associations of specific leaf area with nitrogen absorption rate of roots

Authors

  • Yoko Osone,

    1. Department of Plant Ecology, Forestry and Forest Products Research Institute, Tsukuba, Ibaraki 305-8687, Japan;
    2. Department of Natural Science, International Christian University, Osawa 3-10-2, Mitaka, Tokyo 181-8585, Japan;
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  • Atsushi Ishida,

    1. Department of Plant Ecology, Forestry and Forest Products Research Institute, Tsukuba, Ibaraki 305-8687, Japan;
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  • Masaki Tateno

    1. Nikko Botanical Garden, Graduate school of science, University of Tokyo, Nikko, Tochigi 321-1435, Japan
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Author for correspondence:
Y. Osone
Tel: +81 29 829 8219
Fax: +81 29 873 3211
Email: osone@ffpri.affrc.go.jp

Summary

  • • Close correlations between specific leaf area (SLA) and relative growth rate (RGR) have been reported in many studies. However, theoretically, SLA by itself has small net positive effect on RGR because any increase in SLA inevitably causes a decrease in area-based leaf nitrogen concentration (LNCa), another RGR component. It was hypothesized that, for a correlation between SLA and RGR, SLA needs to be associated with specific nitrogen absorption rate of roots (SAR), which counteracts the negative effect of SLA on LNCa.
  • • Five trees and six herbs were grown under optimal conditions and relationships between SAR and RGR components were analyzed using a model based on balanced growth hypothesis.
  • • SLA varied 1.9-fold between species. Simulations predicted that, if SAR is not associated with SLA, this variation in SLA would cause a 47% decrease in LNCa along the SLA gradient, leading to a marginal net positive effect on RGR. In reality, SAR was positively related to SLA, showing a 3.9-fold variation, which largely compensated for the negative effect of SLA on LNCa. Consequently, LNCa values were almost constant across species and a positive SLA–RGR relationship was achieved.
  • • These results highlight the importance of leaf–root interactions in understanding interspecific differences in RGR.

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