Using flow gauges to determine leaf specific conductance in hybrid poplars under mesic and xeric conditions

Abstract

A study was conducted using sap flow gauges to determine leaf specific conductance (LSC) in hybrid poplars in an environmentally-controlled greenhouse at Swift Current, Saskatchewan. Sap flow rates were compared between CanAm and Walker poplar clones using stem flow gauges. The primary objectives were to verify differences in LSC observed between the clones under moist field conditions in a previous study and to compare the responses in sap flow and LSC within these trees as imposed soil conditions changed from moist to dry. Walker poplars appear to be well-suited to mesic sites, and, under ample soil moisture, perform better than CanAms. However, they are susceptible to mid-season terminal shoot dieback, while CanAm poplars do not seem to be as susceptible. We suspect that this is primarily attributable to a greater LSC of CanAm poplars and possibly achieving better stomatal responses during periods of extended vapor pressure deficits. The gauges were mounted near the base of each tree. Following gauge installation, the trees were watered to field capacity. No additional water was added during the course of the test. Sap flow, leaf water potentials and tree conditions were monitored for 17 days as the soil conditions evolved from moist to dry. Results indicate that the CanAms displayed a greater LSC under moist as well as dry conditions compared to the Walkers. Throughout the testing period, CanAm mid-day leaf water potentials were slightly more negative than for the Walker poplars. Although CanAm poplars appear to be less water efficient than Walkers, they are better able to function and survive during periods of extended vapour pressure deficits.