EFFECTS OF SITE CHARACTERISTICS ON NITROGEN RETRANSLOCATION FROM SENESCING LEAVES

The efficiency of nitrogen recovery before leaf fall in different woody species was studied with respect to the phenology of leaf abscission and to different estimates of nitrogen availability. Among the factors considered, the duration of the abscission period shows the strongest effect on the retranslocation efficiency. The species with gradual leaf fall exhibit lower percentages of nitrogen recovery, probably due to greater unpredictability of the exact time of abscission. Gradual leaf fall seems to be an adaptation to water stress in regions with an arid or semiarid climate. The species that occupy the more xeric sites thus show lower retranslocation rates. By contrast, the factors related to nitrogen availability show no clear effect on the reabsorption efficiency.