Does leaf shedding increase the whole-plant carbon gain despite some nitrogen being lost with shedding?

Authors

  • Shimpei Oikawa,

    1. Graduate School of Life Sciences, Tohoku University, 6-3 Aoba, Sendai 980-8578, Japan;
    2. Present address: Center for Bioresource Field Science, Kyoto Institute of Technology, Kyoto, 616-8354 Japan;
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  • Kouki Hikosaka,

    1. Graduate School of Life Sciences, Tohoku University, 6-3 Aoba, Sendai 980-8578, Japan;
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  • Tadaki Hirose

    1. Department of International Agricultural Development, Tokyo University of Agriculture, Sakuragaoka 1-1-1, Setagoya, Tokyo 156-8902, Japan
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Author for correspondence:
Shimpei Oikawa
Tel: +81 75 8610714
Fax: +81 75 8618418
Email: oikawa@kit.ac.jp

Summary

  • • When old leaves are shed, part of the nitrogen in the leaf is retranslocated to new leaves. This retranslocation will increase the whole-plant carbon gain when daily C gain : leaf N ratio (daily photosynthetic N-use efficiency, NUE) in the old leaf, expressed as a fraction of NUE in the new leaf, becomes lower than the fraction of leaf N that is resorbed before shedding (RN).
  • • We examined whether plants shed their leaves to increase the whole-plant C gain in accord with this criterion in a dense stand of an annual herb, Xanthium canadense, grown under high (HN) and low (LN) nitrogen availability.
  • • The NUE of a leaf at shedding expressed as a fraction of NUE in a new leaf was nearly equal to the RN in the LN stand, but significantly lower than the RN in the HN stand. Thus shedding of old leaves occurred as expected in the LN stand, whereas in the HN stand, shedding occurred later than expected.
  • • Sensitivity analyses showed that the decline in NUE of a leaf resulted primarily from a reduction in irradiance in the HN stand. On the other hand, it resulted from a reduction in irradiance and also in light-saturated photosynthesis : leaf N content ratio (potential photosynthetic NUE) in the LN stand.

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