Wednesday, August 8, 2007
Exhibit Halls 1 and 2, San Jose McEnery Convention Center
Evergreen chaparral shrubs of the Santa Monica Mountains in southern California are typically subjected to a six to nine month period of summer drought and periodic wildfire. Even though both resprouts and adults at the same post-fire microsite are genetically similar, it was hypothesized that the phenotypic characteristics, specifically, the plants’ drought tolerances, would be different. To test this hypothesis, stem segments from both resprouts and adults were subjected to a centrifuge technique in order to determine the percent loss of hydraulic conductivity (PLC) due to embolism. An initial comparison of the PLCs of both resprouts and adults showed that the resprouts (50% PLC = -3.7 MPa) were more vulnerable to water-stress induced embolism than adults (50% PLC = -5.5 MPa). To further explore these data, other physiological tests were stomatal conductance to water vapor diffusion, transpiration rates, predawn and midday water potentials, growth rates, leaf-specific conductivity, xylem-specific conductivity, and estimated vessel implosion resistance. In each case, resprouts were significantly different from adults. Resprouts may have selective traits that allow rapid shoot growth and post-fire reestablishment at the expense of safety from xylem embolism and vessel implosion resistance due to water stress.
