Bole girdling affects metabolic properties and root, trunk and branch hydraulics of young ponderosa pine trees
Jean-Christophe Domec (1, 2) and Michele L. Pruyn (3)
1. Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, NC 27795, USA / 2. Corresponding author () / 3. Department of Biological Sciences, Plymouth State University, Plymouth, NH 03264, USA / Received February 13, 2008; accepted May 20, 2008; published online August 1, 2008
Summary
Effects of trunk girdling on seasonal patterns of xylem water status, water transport and woody tissue metabolic properties
were investigated in ponderosa pine (Pinus ponderosa Dougl. ex P. Laws.) trees. At the onset of summer, there was a sharp decrease in stomatal conductance (gs) in girdled trees followed by a full recovery after the first major rainfall in September. Eliminating the root as a carbohydrate
sink by girdling induced a rapid reversible reduction in gs. Respiratory potential (a laboratory measure of tissue-level respiration) increased above the girdle (branches and upper
trunk) and decreased below the girdle (lower trunk and roots) relative to control trees during the growing season, but the
effect was reversed after the first major rainfall. The increase in branch respiratory potential induced by girdling suggests
that the decrease in gs was caused by the accumulation of carbohydrates above the girdle, which is consistent with an observed increase in leaf mass
per area in the girdled trees. Trunk girdling did not affect native xylem embolism or xylem conductivity. Both treated and
control trunks experienced loss of xylem conductivity ranging from 10% in spring to 30% in summer. Girdling reduced xylem
growth and sapwood to leaf area ratio, which in turn reduced branch leaf specific conductivity (LSC). The girdling-induced
reductions in gs and transpiration were associated with a decrease in leaf hydraulic conductance. Two years after girdling, when root-to-shoot
phloem continuity had been restored, girdled trees had a reduced density of new wood, which increased xylem conductivity and
whole-tree LSC, but also vulnerability to embolism.
