WWRC 90-26
Stomatal Conductance Patterns and Environment in High Elevation Phreatophytes of Wyoming
Abstract
High-elevation (2305 m) phreatophytes (cottonwood, Populus angustifolia James, and willows,
Salix monticola Nutt. and Salix exigua Bebb) in southeastern Wyoming commonly showed
a pattern of increasing stomatal conductance (g1) throughout the day, despite minimum
leaf water potentials (y1) as low as -2.7 MPa. Diurnally,
light and leaf temperature were the most important variables influencing g1 but there
were also threshold values of y1 and leaf-to-air vapor pressure
deficit for stomatal closure. Seasonally, maximum daily g1 (gmax) was similar
between species, was positively related to minimum air temperature the previous night, and showed a
threshold response to soil temperature. Two types of evidence existed for large soil-to-leaf
conductances (gs-1) and for liquid water being available to the roots. The first was no
change in y1 despite increasing transpiration during the afternoon.
The second was rapid evening recovery of y1 often to values higher
than mean soil water potential to 60-cm depth. The combination of low atmospheric pressures at high
elevation, large gs-1 and access to a water table may explain how these phreatophytes
attained gmax of 0.8-0.9 mol m-2 s-1 much higher than gmax
of low-elevation phreatophytes or high-elevation nonphreatophytes.
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