The influence of nitrogen supply on growth and internal recycling of nitrogen in young Nothofagus fusca trees

Abstract

The effect of nitrogen supply on biomass, and nitrogen storage and remobilisation, was investigated in young Nothofagus fusca (Hook f.) Oerst. trees growing in pots while irrigated with nutrient solutions containing 0.5 (low nitrogen, LN), 3 (medium nitrogen, MN) and 6 (high nitrogen, HN) mM nitrogen. During the first annual growth cycle, nitrogen supply was labelled with ¹⁵ N. By mid-autumn of the second annual cycle, dry weights of whole tree, stem, leaves and roots for trees in the HN and MN treatments were over 10-fold greater than the weights for trees in the LN treatment. Nitrogen was stored in roots and remobilised for new leaf and stem growth during spring. In summer, remobilised nitrogen comprised approximately 40% of the total nitrogen in leaves and stems for trees in all treatments. Nitrogen uptake for trees in the HN and MN treatments continued during the winter dormant period, and accounted for approximately half the total nitrogen acquired during the first cycle. Storage of nitrogen in roots (a deciduous characteristic), and the independence of nitrogen remobilisation from leaf senescence and significant winter uptake of nitrogen (both evergreen characteristics), suggest that the leaf phenology of N. fusca allows the species to maximise nitrogen acquisition from low fertility soils to enhance productivity.