Using flow gauges to determine stem and root conductance in hybrid poplars.
A study was conducted using sap flow gauges to determine stem and root conductance in hybrid poplars at two sites near Swift Current, Saskatchewan. At the Rushlake site, sap flow rates were compared between CanAm and Walker poplars using Dynamax (Model SGA-10) stem flow gauges. The primary objective was to determine if the difference in susceptibility to midsummer terminal shoot dieback in Walker and CanAm poplar clones could be attributed to leaf-specific conductance. Walker poplars appear to be well-suited to mesic sites and, under good soil moisture conditions, perform better than CanAm . 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 leaf-specific conductance (LSC) of CanAm poplars. As a tertiary cause, perhaps CanAm poplars achieve a more complete stomatal closure during periods of extended vapor pressure deficits. The gauges were mounted at the distal ends (where the shoot diameter is about 10 mm) of actively growing branches near the crown of each tree. For a period of 14 days, the sap flow rates of each tree were measured. Preliminary results indicate that CanAms did indeed have a greater LSC and showed higher stem flow rates than Walker poplars. Under the study conditions at the Rushlake site, air temperatures were not of sufficient magnitude to determine differences in leaf stomatal closure between the CanAm and Walker trees. The LSC characteristics, however, would have benefited the CanAm poplars in functioning under extended vapor pressure deficits. A secondary objective was to determine if differences in root conductances of poplars subjected to varying saline conditions were possible to measure using sap flow gauges. Although great care must be taken during gauge installation on tree roots, we found it is possible to measure root sap conductance on trees subjected to varying levels of salinity.
leaf specific conductance
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