Nitrogen retranslocation, allocation, and utilization in bare root Larix olgensis seedlings

We quantified biomass accumulation and nitrogen (N) retranslocation, allocation, and utilization of Changbai larch (Larix olgensis) seedlings subjected to four fertilization treatments (24, 59, 81, 117 kg·ha⁻¹ N) with an unfertilized control during summer and autumn 2009. Ammonium phosphate (18-46-0) was the fertilizer used in all treatments. On both sampling dates, the needles had greater biomass and N content than new (2009) stems and old (2008) stems, and coarse, medium and fine roots (diameters of >5, 2–5 mm, and 0–2 mm, respectively). Higher N concentration was observed in old stems and coarse roots than that in new stems and medium roots. In mid-summer, fine roots had higher N concentration than coarse roots. The treatment with 24 kg·ha⁻¹ N had the greatest biomass and N content in needles and old stems, and highest net N retranslocation (NRA) and amount of N derived from soil. On September 21, no N translocation was observed, while the treatment with 24 kg·ha⁻¹ N had the highest N utilization efficiency and fertilizer efficiency. Vector analysis revealed that all four fertilization treatments induced N excess relative to the control. The treatments with 59, 81, 117 kg·ha⁻¹ N induce N excess compared with treatments at 24 kg·ha⁻¹ N. We conclude that the traditional local fertilizer application rates exceeded N requirements and N uptake ability for Changbai larch seedlings. The application rate of 24 kg·ha⁻¹ N is recommended.