NARROW HYBRID ZONE BETWEEN 2 SUBSPECIES OF BIG SAGEBRUSH (ARTEMISIA-TRIDENTATA, ASTERACEAE) - VI - RESPIRATION AND WATER POTENTIAL

Respiration and stem water potential (Psi) were examined in parental a nd hybrid big sagebrush (Artemisia tridentata Nutt. ssp. tridentata an d Artemisia tridentata Nutt. ssp. vaseyana (Rydb.) Beetle) grown in co mmon gardens within each parental zone and in the hybrid zone. Plants were sampled in July, August, and September, i.e., immediately before, during, and after flowering. The habitats differed from one another, and there were significant garden by date interactions. The source pop ulations also differed significantly from one another. There were no s ignificant garden by source interactions. Hybrid plants had intermedia te respiration rates and did not suffer greater water stress than pare ntal plants. Hybrid plants showed no apparent decrease in adaptation i n the important physiological traits respiration and water stress in t he hybrid zone.