© 2007 Heron Publishing—Victoria, Canada
Within-canopy nitrogen and photosynthetic gradients are unaffected by soil fertility in field-grown Eucalyptus globulus
Tarryn L. Turnbull (1, 2, 3), Natalie Kelly (4), Mark A. Adams (3) and Charles R. Warren (5)
1. School of Forest and Ecosystem Science, University of Melbourne, Water Street, Creswick, VIC 3363, Australia / 2. Corresponding author (t.turnbull@unsw.edu.au) / 3. Present address: Laboratory for Ecosystem Science and Sustainability, School of Biological Earth and Environmental Sciences,
University of New South Wales, NSW 2052, Australia / 4. Australian Government Antarctic Division, Kingston, Tasmania, 7050, Australia / 5. School of Biological Sciences, Heydon-Laurence Building A08, University of Sydney, NSW 2006, Australia / Received December 18, 2006; accepted March 1, 2007; published online August 1, 2007
Summary
A significant and well-supported hypothesis is that increased growth following nitrogen (N) fertilization is a function of
the relationships among photosynthesis, tissue N content and the light environment—specifically, the within-canopy allocation
of N among leaves and the within-leaf allocation of N between Rubisco and chlorophyll. We tested this hypothesis in a field
trial that included annual applications of N,P,K fertilizer (from planting) to a Eucalyptus globulus Labill. plantation growing on uniform leached sands. Growth of 4-year-old E. globulus increased significantly in response to fertilization. Leaf N and phosphorus concentrations were 0.1–0.5 g m–2 and 0.4–0.5 g m–2 higher in fertilized trees compared to unfertilized trees, respectively. Stomatal conductance (gs) at the maximum photosynthetic rate (Amax) was between 0.2 and 0.4 mol m–2 s–1 higher in fertilized trees, but Amax and the concentration of Rubisco (Ruba) were unaffected by fertilization. This seeming paradox, where there was no response of Amax to fertilization despite increases in gs and leaf N concentration, was explained by reduced in vivo specific activity of Rubisco in fertilized trees. Acclimation
to light, measured by redistribution of N between Rubisco and chlorophyll, was unaffected by fertilization. Distribution of
leaf N followed irradiance gradients, but Amax did not. Maximum photosynthetic rate was correlated with leaf N concentration only in unfertilized trees. These findings
indicate that the relationships among photosynthesis, N and the light environment in E. globulus are affected by N,P,K fertilization.
Keywords:
chlorophyll, maximum photosynthetic rate, phosphorus, photosynthetic biochemistry, relative irradiance, Rubisco, stomatal
conductance.
