Araucaria cunninghamii Seedling Response to Different Forms and Rates of ~(15)N-Labelled Fertiliser

摘要

Nitrogenous fertilisers are under consideration for promoting the growth of nursery-reared hoop pine (Araucaria cunninghamii Aiton ex A. Cunn) seedlings in the establishment phase of second rotation (2R) plantations. Using ~(15)N-labelled fertilisers, we investigated the effect of different forms (ammonium sulphate, ammonium nitrate, potassium nitrate and urea) and rates of application (0, 150 and 300 mg N kg~(-1) dried soil) of fertilisers on the growth, ~(15)N recovery and carbon isotope composition (δ~(13)C) of hoop pine seedlings in a 12-month glasshouse trial in southeast Queensland, Australia. The ~(15)N-labelled fertilisers were applied to nursery-reared hoop pine seedlings, which were then grown in pots, containing ca. 1.2 kg dried soil, under well watered conditions for 12 months. Four seedlings from each treatment were harvested at 4-month intervals, divided into roots, stem and foliage, with a further subdivision for new and old foliage, and then analysed for ~(15)N, total N, δ~(13)C and total C. There was no significant response in the seedling growth to the form or rate of application of nitrogen (N) fertiliser within the 12-month period, indicating that the seedlings did not experience N deficiency when grown on second rotation hoop pine soils. While the combined ~(15)N recovery from soil and plant remained at around 70% throughout the experiment, the proportion of ~(15)N recovered from the plants increasing steadily over time. Nitrate containing fertilisers at 150 mg N kg~(-1) soil gradually increased seedling foliage δ~(13)C over the 12-month period, indicating an increase in seedling water use efficiency.