© 2007 Heron Publishing—Victoria, Canada
Uptake of nitrate, ammonium and glycine by plants of Tasmanian wet eucalypt forests
C. R. Warren (1–3) and P. R. Adams (4)
1. School of Forest and Ecosystem Science, University of Melbourne, Water Street, Creswick VIC 3363, Australia / 2. Present address: School of Biological Sciences, University of Sydney, NSW 2006, Australia / 3. Corresponding author (charles.warren@bio.usyd.edu.au) / 4. Division of Forest Research and Development, Forestry Tasmania, 79 Melville Street, Hobart TAS 7001, Australia / Received March 6, 2006; accepted June 8, 2006; published online December 1, 2006
Summary
A central assumption of ecosystem N cycling has been that organic N must be converted to inorganic N to be available for plant
uptake, but this has been questioned by recent studies. We examined uptake of nitrate, ammonium and the amino acid glycine
in three species from Eucalyptus obliqua L’Her. wet forest in Tasmania, south-eastern Australia, to test the hypothesis that all three species can take up glycine,
and to compare rates of glycine uptake with rates of uptake of nitrate and ammonium uptake. The alternative hypothesis that
species vary in their preference for nitrate, ammonium and glycine (“niche differentiation”) was also examined. Measurements
were made on the canopy dominant Eucalyptus obliqua, and two rain forest tree species found in the understory or as sub-dominants of the canopy, Nothofagus cunninghamii (Hook.) Oerst. and Phyllocladus aspleniifolius (Labill.) Hook.f. Nitrogen uptake was examined in situ with attached roots placed in uptake solutions containing equimolar
concentrations (100 µmol l–1) of 15N-nitrate, 15N-ammonium and 2-13C215N-glycine. Species did not differ in their preference for different forms of N (species × N form interaction, P > 0.05), and thus there was no evidence of niche differentiation. In all species, rates of uptake were highest for ammonium
(11 ± 5 µmol gDM–1 h–1; mean ± SD, n = 108), uptake of glycine occurred at less than half this rate (4.4 ± 2.6 µmol gDM–1 h–1), whereas uptake of nitrate occurred at one-tenth of this rate (0.9 ± 1.2 µmol gDM–1 h–1). The strong positive relationship between 15N and 13C uptake indicated that at least 72% of glycine-N was taken up intact. These findings indicate the potential for considerable
uptake of organic N in the field.
Keywords:
amino acid, Eucalyptus obliqua, nitrogen, Nothofagus cunninghamii, organic N, Phyllocladus aspleniifolius, wet forest.
