Reproductive growth during drought in Artemisia tridentata Nutt

Artemisia tridentata Nutt, is a drought-tolerant shrub that expands inflorescences during summer and autumn, even though xylem pressure potentials may be less than -5.0 MPa. Supplemental watering increased total inflorescence biomass and the biomass of floral heads over 450 and 550%, respectively. Inflorescences displayed positive net photosynthesis until xylem pressure potentials decreased below -5.0 MPa. Growth of inflorescences was not dependent on carbon imported from vegetative leaves; removal of all leaves on vegetative branches did not change inflorescence biomass, and 14CO2 fixed by adjacent vegetative branches was not transferred into inflorescences. Expanding inflorescences during summer may enhance competitive ability because biomass can be allocated solely towards vegetative growth during spring, increasing the capacity of Artemisia tridentata to acquire resources when they are most abundant. Conversely, inflorescences that are photosynthetically self-sufficient can better respond to favourable soil moisture or intermittent precipitation during summer, because photosynthesis can be increased without investing resources into further vegetative growth.