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.
Impact of Land use and Cover Change on Soil Organic Carbon and Total Nitrogen Storage in the Helmand River Basin