Abstract Title

Xylem Anatomy and Hydraulic Conductivity of Psuedotsuga menziesii var. glauca Along an Elevation Gradient

Abstract

The causes of lower treelines in the Intermountain West are not entirely understood. Little is known about how conifer trees adjust their structural morphology at lower treeline as they experience increased drought-conditions with decreasing elevation. We hypothesized that as elevation decreases, hydraulic transport capability decreases, because trees design their xylem structure more for safety against cavitation rather than for transport efficiency under drier conditions. To test this hypothesis, branch samples were collected from Rocky Mountain Douglas-fir trees (Pseudotsuga menziesii var. glauca) along an elevation gradient from 1700 m elevation to 2100 m elevation. Cross sections were then sliced off of the Douglas-fir tree branches and placed onto microscope slides. The cross sections were then imaged with a confocal microscope and uploaded to an image analysis program (ImageJ) . Using ImageJ, the number of growth rings, ring width (mm), number of trachieds, trachied area (mm), and trachied density were determined for each cross section. We found that Rocky Mountain Douglas-fir make adjustments in various hydraulic and morphological parameters at the branch-level with decreasing elevation. Branches at lower treeline had structural characteristics that suggested greater resistance to hydraulic dysfunction created by increasing xylem tension, but also exhibit trade-offs in decreased water transport efficiency. These elevation gradients had a clear effect on branch hydraulic transport ability and morphological traits.

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Xylem Anatomy and Hydraulic Conductivity of Psuedotsuga menziesii var. glauca Along an Elevation Gradient

The causes of lower treelines in the Intermountain West are not entirely understood. Little is known about how conifer trees adjust their structural morphology at lower treeline as they experience increased drought-conditions with decreasing elevation. We hypothesized that as elevation decreases, hydraulic transport capability decreases, because trees design their xylem structure more for safety against cavitation rather than for transport efficiency under drier conditions. To test this hypothesis, branch samples were collected from Rocky Mountain Douglas-fir trees (Pseudotsuga menziesii var. glauca) along an elevation gradient from 1700 m elevation to 2100 m elevation. Cross sections were then sliced off of the Douglas-fir tree branches and placed onto microscope slides. The cross sections were then imaged with a confocal microscope and uploaded to an image analysis program (ImageJ) . Using ImageJ, the number of growth rings, ring width (mm), number of trachieds, trachied area (mm), and trachied density were determined for each cross section. We found that Rocky Mountain Douglas-fir make adjustments in various hydraulic and morphological parameters at the branch-level with decreasing elevation. Branches at lower treeline had structural characteristics that suggested greater resistance to hydraulic dysfunction created by increasing xylem tension, but also exhibit trade-offs in decreased water transport efficiency. These elevation gradients had a clear effect on branch hydraulic transport ability and morphological traits.