Influence of nitrogen and phosphorus supply on foliage growth and internal recycling of nitrogen in conifer seedlings (Prumnopitys ferruginea)

The dynamics of internal cycling of nitrogen were studied in the southern hemisphere conifer miro [Prumnopitys ferruginea (G. Benn. ex D. Don) de Laub.], which has an indeterminate growth habit. In a 2-year experiment, P. ferruginea seedlings were supplied with nutrient solutions consisting of two different concentrations of nitrogen (5 and 0.5 mM) and phosphorus (1.33 and 0.133 mM) in the first year, and two concentrations (5 and 0.5mM) of a ¹⁵N-labelled nitrogen solution in the second year. Growth and nitrogen content of new foliage were shown to be largely dependent on seedling nitrogen status at the end of the first year, and only weakly dependent on nutrient supply in the second. An average of 70% of total nitrogen in new foliage was remobilised from storage in the first 63 d after flushing began. The remainder of new-foliage nitrogen was derived by root uptake from the nutrient supply in the second year. There was some response of nitrogen uptake to high nitrogen supply in the second year where seedlings had been nitrogen deficient at the end of the first year. However, it was concluded that the indeterminate growth habit of P. ferruginea did not distinguish its pattern of nitrogen storage and remobilisation from that of determinate conifers.