Water relations of white spruce (Piceaglauca (Moench) Voss) at tree line in north central Alaska

Abstract

Factors affecting xylem pressure potential and stomatal behavior during the growing season were studied in white spruce (Picea glauca (Moench) Voss) at tree line in the central Brooks Range of northern Alaska. Leaf conductance and xylem pressure potentials were low during days of moderate and high evaporative demand, even though soil moisture was near field capacity. Boundary line diagrams, regression analysis, and laboratory experiments indicate that stomata are sensitive to changes in vapor pressure deficit and xylem pressure potential. A correlation between resistance to water flow through the tree and soil temperature suggests that soil temperatures less than 9.degree. C are associated with increased resistance to water flow and may partially explain the position of white spruce tree line in northern Alaska.