PARENT SESSION
Oral Session 10: Physiology I: Temperature, Light, and Growth.
Presiding: C Knight
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room C 123.
Juniperus occidentalis and Austrocedrus chilensis: These north-south cousins live in similar environments but their ecophysiology is very different.
Bond, Barbara*,1, Schlichter, Tomas2, Fernandez, Maria 2, Letourneau, Federico 2, 1 Department of Forest Science, Corvallis, OR2 Instituto Nacional de Tecnologia y Agropecuaria, San Carlos de Bariloche, Argentina
ABSTRACT- Juniperus occidentalis (western juniper) and Austrocedrus chilensis (Cipres de la cordillera) occupy similar niches in the northern and southern hemispheres, respectively. The two species grow at similar latitudes on the western side of their continents; both extend farther into rain shadow caused by western mountain ranges than any other tree species in their regions. Both are members of the cupressaceae, and they share a similar morphology, including pyramidal crown with typical maximum heights of about 20-25m, a scale-like leaf structure and compact form. Both species tend to grow in rocky or sandy soils as isolated individuals or low-density communities. Given these similarities, one might expect the to species to have similar ecophysiological characteristics. However, when we compared measurements of water relations, photosynthesis, and xylem vulnerability to cavitation, we found striking differences. Midday water potential of A. chilensis rarely falls below -1.8 MPa, whereas that of J. occidentalis has often been measured below -3.0 MPa. Maximum stomatal conductance and photosynthesis are similar, but it appears that J. occidentalis is capable of much greater net C assimilation over time due to its ability to maintain open stomata at low water potentials. Stemwood of A. chilensis is much more vulnerable to cavitation than that of J. occidentalis. Regeneration of A. chilensis is slow and intermittent, in part because seedlings do not survive unless they shaded for several years, while J. occidentalis is capable of rapid regeneration. Why hasn't A. chilensis, or any other tree in its region, evolved the drought-tolerant physiological characteristics of J. occidentalis? We discuss this, and these characteristics leave A. chilensis ecosystems vulnerable to invasion by exotic woody species.
Key words: photosynthesis, ecophysiology