PARENT SESSION
Poster Session #40: Water Relations I.
Wednesday, August 7. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Micro-variation of ¹³C in tree rings of Ponderosa pine from aouthern Arizona.

Leavitt, Steven^*,1, Wright, Wm.¹, Hemming, Debbie^1,2, Long, Austin¹, ¹ University of Arizona, Tucson, Arizona² Weizmann Institute of Science, Rehovot, Israel

ABSTRACT- The mechanistic relationship between plant ¹³C and water-use efficiency forms the basis for commonly observed correlations between tree-ring ¹³C and plant water status (including rainfall, soil moisture, humidity, drought stress). Analysis of fine subdivisions of tree rings may therefore reveal minute details of environmental conditions and plant/environment interactions over the course of the growing season. To examine these detailed variations, we microtomed 50-100-micron-thick subdivisions of the 1998 growth ring from several Pinus ponderosa trees sampled in the Santa Catalina Mts. near Tucson. One of these trees had also been exposed to a CO₂ isotope tracer pulsed in for several days in mid-growing season to follow the fate of assimilated carbon. Analysis of the whole wood tissue of two trees that did not receive the tracer revealed highest ¹³C values near the beginning of the growing season, and lowest values at or near the end. Analysis of several samples from the tree that received the tracer showed a similar pattern but with a more pronounced mid-season minimum in the lower bole; the upper bole exhibited much more variability, including some highly ¹³C-enriched values at the beginning of the growing season. The isotope patterns seem to variously reflect influences of local seasonal climate conditions, possible microclimate difference among individual trees, and anomalies that may be related to stored versus new photosynthate contribution to growth.

KEY WORDS: pinus ponderosa, carbon isotopes, water relations, tree rings