Abstract: A field experiment was conducted to study the effects of nitrogen (N) topdressing on the biomass accumulation and nutrient concentration and storage in different organs of two-year-old eucalyptus. Comparing with the control, N topdressing increased the eucalyptus biomass by 24.2 %. Branch had the highest increment (38.2%), while leaf had the lowest one. The nutrient uptake under N topdressing was improved significantly, with the order of P>K>N>Mg>Ca>Si. Leaf had the highest contents of N, P, Mg, and Si; trunk had the highest storage of K; while branch had the most significant increase of nutrient concentration and storage. The N, P, and K were recycled mainly through internal flux, with 73.8% of N, 79.1% of P, and 72.9% of K in leaf transferred back to the plant before leaf fallen, and the external flux of these three nutrients only occupied 14.8%, 7.7%, and 8.6% of their total storage in the tree, respectively. The Ca, Mg and Si were the external flux elements, especially for Ca. 89.2% of Ca in leaf was cycled in external flux, accounting for 25.9% of its total storage in the tree.

Key words: Eucalyptus, nitrogen topdressing, biomass, nutrient concentration, nutrient storage, stable isotopes, gladius, jumbo squid, migration patterns, feeding habits.