Prunus species were grown on the roof of the biology building at Occidental College under uniform conditions. While the species were well-watered, initial measurements of average segment diameter, wood density, total leaf area from the branch, specific leaf area, leaf thickness, xylem water potential, and hydraulic conductivity both before and after the xylem embolism flush, were recorded for each of the seven species. One key finding from the initial measurement was that the post-flush Kh was much greater for the Bing Cherry than any other species, and it had the second highest percent embolism which suggests that there is a trade-off amongst Prunus species between high values of hydraulic conductivity and xylem safety. The greater the amount of water the tree moves, the more susceptible it is to embolism. After all of the initial measurements were made, the trees endured a 10 day drought period. Xylem water potential, stomatal conductance, and leaf chlorophyll fluorescence were measured daily at noon in order to assess the plants’ overall health throughout the drought period. Both Native Plum and Bing Cherry, which are native to regions with relatively high rainfall, had the greatest changes in xylem water potential, reflecting the greatest stress during drought. On the other hand, the evergreen species Catalina and Holly Leaf Cherry had lower stomatal conductance and lower photosynthetic efficiency than the other species, supporting the hypothesis that habitat aridity is associated with the evolution of greater water use efficiency at the cost of lower productivity.

Support provided by: Howard Hughes Medical Institute Undergraduate Science Education Grant