Drought tolerance mechanisms and resource allocation in Artemisia tridentata Nutt. ssp. tridentata

Artemisia tridentata is a drought-tolerant shrub that expands inflorescences during summer and autumn, even though plant water potentials may exceed {dollar}-{dollar}5.0 MPa. I examined the mechanisms that enable A. tridentata to tolerate drought and the seasonal allocation of resources to vegetative and reproductive growth. Artemisia tridentata was able to remain active during drought because of a concurrent decline in water potential and osmotic potential that maintained turgor at 1.5 MPa. The decrease in osmotic potential was due to passive concentration of solutes within the leaf. The only solutes accumulating with water stress were proline and a cyclitol, both considered compatible solutes. Pressure-volume analysis was not appropriate for analysis of water relations in A. tridentata because of errors introduced by rehydration of plant material.; Water stress limited allocation to reproductive structures. Growth of inflorescences was not dependent upon carbon imported from vegetative leaves; removal of all vegetative leaves caused no change in final inflorescence biomass. Radiotracer ({dollar}sp{lcub}14{rcub}{dollar}CO{dollar}sb2{dollar}) applied to vegetative leaves was not translocated into inflorescences, and inflorescences were capable of positive net photosynthesis until plant water potential decreased below {dollar}-{dollar}5.0 MPa. Expanding inflorescences during summer may enhance the competitive ability of A. tridentata because allocation during spring can be directed towards vegetative growth and resource acquisition.; Vegetative biomass was not altered by supplemental water; development of vegetative structures was completed before water potentials fell below {dollar}-{dollar}3.0 MPa. Conversely, supplemental water during drought increased biomass of inflorescence leaves and floral heads over 100 and 700%, respectively. Lowered stomatal conductance during summer conserved water but simultaneously decreased photosynthesis. Drought did not alter construction costs of tissues or nitrogen and carbon invested in vegetative or reproductive biomass. But the {dollar}delta{dollar} {dollar}sp{lcub}13{rcub}{dollar}C of inflorescence leaves and floral heads was less negative for controls, indicating greater water use efficiency and higher water costs of construction for these structures.