© 2001 Heron Publishing—Victoria, Canada
Morphological and physiological adjustment to N and P fertilization in nutrient-limited Metrosideros polymorpha canopy trees in Hawaii
S. Cordell (1, 2), G. Goldstein (1), F. C. Meinzer (3, 4) and P. M. Vitousek (5)
1. Department of Botany, University of Hawaii, 3190 Maile Way, Honolulu, HI 96822, USA / 2. USDA Forest Service, 23 E. Kawili St., Hilo, HI 96720, USA / 3. Hawaii Agriculture Research Center, 99-193 Aiea Heights Drive, Aiea, HI 96701, USA / 4. USDA Forest Service, Forestry Sciences Laboratory, 3200 SW Jefferson Way, Corvallis, OR 97331, USA / 5. Department of Biological Sciences, Stanford University, Stanford, CA 94305, USA / Received October 18, 1999
Summary
Leaf-level studies of Metrosideros polymorpha Gaud. (Myrtaceae) canopy trees at both ends of a substrate age gradient in the Hawaiian Islands pointed to differential patterns
of adjustment to both nutrient limitation and removal of this limitation by long-term (8–14 years) nitrogen (N), phosphorus
(P) and N + P fertilizations. The two study sites were located at the same elevation, had similar annual precipitation, and
supported forests dominated by M. polymorpha, but differed in the age of the underlying volcanic substrate, and in soil nutrient availability, with relatively low N at
the young site (300 years, Thurston, Hawaii) and relatively low P at the oldest site (4,100,000 years, Kokee, Kauai). Within
each site, responses to N and P fertilization were similar, regardless of the difference in soil N and P availability between
sites. At the young substrate site, nutrient addition led to a larger mean leaf size (about 7.4 versus 4.8 cm2), resulting in a larger canopy leaf surface area. Differences in foliar N and P content, chlorophyll concentrations and carboxylation
capacity between the fertilized and control plots were small. At the old substrate site, nutrient addition led to an increase
in photosynthetic rate per unit leaf surface area from 4.5 to 7.6 μmol m–2 s–1, without a concomitant change in leaf size. At this site, leaves had substantially greater nutrient concentrations, chlorophyll
content and carboxylation capacity in the fertilized plots than in the control plots. These contrasting acclimation responses
to fertilization at the young and old sites led to significant increases in total carbon gain of M. polymorpha canopy trees at both sites. At the young substrate site, acclimation to fertilization was morphological, resulting in larger
leaves, whereas at the old substrate site, physiological acclimation resulted in higher leaf carboxylation capacity and chlorophyll
content.
Keywords:
chlorophyll content, leaf level traits, nutrient limitation, photosynthesis.
