title: Foliage nitrogen turnover: differences among nitrogen absorbed at different times by Quercus serrata saplings.
abstract: OBJECTIVE
  Nitrogen turnover within plants has been intensively studied to better understand nitrogen use strategies. However, differences among the nitrogen absorbed at different times are not completely understood and the fate of nitrogen absorbed during winter is largely uncharacterized. In the present study, nitrogen absorbed at different times of the year (growing season, winter and previous growing season) was traced, and the within-leaf nitrogen turnover of a temperate deciduous oak Quercus serrata was investigated.
  
  
  METHODS
  The contributions of nitrogen absorbed at the three different times to leaf construction, translocation during the growing season, and the leaf-level resorption efficiency during leaf senescence were compared using (15)N.
  
  
  RESULTS
  Winter- and previous growing season-absorbed nitrogen significantly contributed to leaf construction, although the contribution was smaller than that of growing season-absorbed nitrogen. On the other hand, the leaf-level resorption efficiency of winter- and previous growing season-absorbed nitrogen was higher than that of growing season-absorbed nitrogen, suggesting that older nitrogen is better retained in leaves than recently absorbed nitrogen.
  
  
  CONCLUSIONS
  The results demonstrate that nitrogen turnover in leaves varies with nitrogen absorption times. These findings are important for understanding plant nitrogen use strategies and nitrogen cycles in forest ecosystems.
authors.affiliation: Graduate School of Life Science, Tohoku University, Aoba, Sendai, 980-8578, Japan. m_ueda@m.tohoku.ac.jp
authors.forename: Miki U
authors.initials: MU
authors.lastname: Ueda
authors.forename: Eri
authors.initials: E
authors.lastname: Mizumachi
authors.forename: Naoko
authors.initials: N
authors.lastname: Tokuchi
mesh_terms: D000042:Absorption; D001692:Biological Transport; D002473:Cell Wall / Q000737:chemistry / Q000378:metabolism; D009584:Nitrogen / Q000032:analysis / Q000378:metabolism*; D058458:Nitrogen Cycle; D009587:Nitrogen Isotopes / Q000032:analysis; D018515:Plant Leaves / Q000254:growth & development / Q000378:metabolism*; D029963:Quercus / Q000254:growth & development / Q000378:metabolism*; D012621:Seasons; D014197:Trees / Q000378:metabolism
chemical_list: D009587:Nitrogen Isotopes; D009584:Nitrogen