PARENT SESSION
Oral Session #106: Plant Ecology: Global Climate Change.
Presiding: D. Breshears
Friday, August 9. 9:00 AM to 12:00 PM. Grand Ballroom East, Radisson.

Variability in carbon and nitrogen isotope composition of bristlecone pine leaves along an altitude gradient .

Ababneh, Linah^*,1, ¹ Graduate Associate in Research, Tucson, AZ

ABSTRACT- Pinus longeava (bristlecone pine) is a remarkable species that achieves unparalleled antiquity and may be the first tree species to have exhibited CO₂ fertilization effects, but study of its ecophysiology is still in its infancy. In this project, I examined (1) variability in carbon and nitrogen in trees at sites separated by 500 m elevation, and (2) climatic effects on variability of carbon and nitrogen isotopic composition.Pinus longeava needles from the 2000 and 1998 cohorts were sampled in the White Mountains of California, from 4 trees at Methuselah Walk (3100 m) and 4 trees at Sheep Mountain (3650 m) in July 2001.Carbon and nitrogen stable isotope composition, C and N concentrations, and C/N ratios were analyzed on finely pulverized whole-leaf tissue. Leaf ¹³C and ¹⁵N were not significantly correlated. For the wet year (1998), ¹³C did not differ between elevations, but ¹³C was significantly different in the dry year (2000) between the high and low sites. Leaf ¹⁵N values in both the wet and the dry year, however, were different between elevations. There is a ¹⁵N increase of about 1.1‰ from low to high elevation, and a ¹³C enrichment of about 1‰with increasing elevation. The latter observation agrees with a previous elevational study using tree rings, and the ¹⁵N results are the first reported for Pinus longeava .C/N ratios differed between elevations for both the wet and dry year.At each site the dry year had a lower C/N ratio, indicating seasonal climate variability influences the ratio of carbon and nitrogen assimilation. Further research will establish relationships between leaf composition of these parameters and those of tree-ring whole wood and cellulose.

KEY WORDS: Pinus longeava, CO₂ , Nitrogen , Stable Isotopes