PARENT SESSION
Poster Session 1: Photosynthesis and Water Relations
Monday, August 8, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

The effect of microsite on water relations of Salix lasiolepis.

Harsh, Shannon^*,1, Roth, Allison¹, Taylor, Dustin¹, Swift, Cheryl¹, ¹ Whittier College, Whittier, CA

ABSTRACT- Studies of dioecious plants have suggested that females inhabit moister microsites than males to offset reproduction costs. This study examines the relationship between surface water availability, wood density, and the distribution of male and female Arroyo willow individuals in a 0.24 km reach of the Tujunga River in the San Gabriel Mountains (California). We surveyed stream cross sections and recorded elevation, along with the number and sex of Arroyo willow individuals within 1.0 m on either side of the survey transect. Cuttings were taken from each individual and wood density was determined. We expected to find more female Arroyo willow individuals at elevations closer to the thalwag. We also predicted that increased surface water availability would result in decreased wood density in female individuals as a result of increased vessel lumen to wall ratios. Preliminary results indicate that elevation does not affect the ratio of male to female individuals, and there are no differences in wood density between males and females. Low summer discharge in the Tujunga River places individuals under water stress, regardless of where they occur in the stream channel, and therefore all individuals may rely more on ground water than on surface water and face similar constraints on xylem construction as a result. Studies have suggested that woody riparian species rely more on ground water than surface water, and our results support this; however, the lack of difference in wood density suggests that females inhabiting moist microsites do not benefit in terms of resources allocated to water transport.

Key words: Water relations, Salix lasiolepis