Xylem Conductivity of vegetative and Reproductive Stem Terminals of Artemisia tridentata Nutt..

Artemisia tridentata ssp. tridentata is a tall perennial native shrub that occurs widely over many western states. Stems exhibit a regular pattern in which numerous stem terminal shoots elongate rapidly in spring and early summer while many vegetative stem terminal branches eventually produce flowers and seeds in late autumn. Stem samples were taken from June to November, 2015. Prior to August 7, most stem terminals only had leaves on branches (vegetative stem terminals). As the season progressed, vegetative stem terminals produced flowers (reproductive stem terminals). Stem terminals that eventually produce flowers and seeds are determinate and die at the end of the growing season. However, if stem terminals produce at least one vegetative branch, these vegetative (indeterminate) branches may remain alive, potentially elongating the following year. For 18 stem terminal samples collected from August 7 to November 23, only three stem terminals were indeterminate. All other stem terminals were determinate. Xylem conductivities, at the junction of the 2015 stem terminals and 2014 growth, were similar at nearly 1.3 g cm MPa^–1 s^–1. In contrast, mean xylem conductivities, at stem terminals of indeterminate and determinate stem terminals, were 0.149 and 0.0015 g cm MPa^–1 s^–1, respectively. The high xylem conductivities for stem terminals of indeterminate stem terminals coincide with actively growing stem terminals, while the lower xylem conductivities for stem terminals of determinate stem terminals coincide with eventual death of these stem terminals. [ABSTRACT FROM AUTHOR]