Although nitrogen turnover within plants has been studied intensively, the fate of N absorbed at different times and particularly over winter is not completely understood. Ueda et al. trace N absorbed at different times of the year in a temperate deciduous oak, Quercus serrata, and find that N absorbed in winter and in the previous growing season contribute significantly to leaf construction. Leaf-level resorption efficiency of winter and previous-season N is higher than that of current-season-absorbed N, suggesting that older N is better retained in leaves than that which is more recently absorbed.
