WWRC 84-23
Autumn Stomatal Closure in Six Conifer Species of the Central Rocky Mountains
Abstract
Environmental and water relations parameters
during fall were monitored for six conifer tree species common to the central Rocky Mountains growing naturally
at the same location (Pinus contorta, Pinus ponderosa, Pinus
flexilus, Pseudotsuga menziesii, Abies lasiocarpa, Picea engelmannii). Subsequent to what appeared to be the beginning of seasonal stomatal closure, leaf conductance to water
vapor declined sharply following the onset of freezing air
temperatures at night. A coincident rapid decline in morning xylem pressure potentials (yp) also occurred which resulted in values that were considerably below afternoon
yp. Continuing decreases in maximum leaf conductance
during the day were highly correlated with corresponding
decreases in minimum nocturnal air temperatures of the
preceding night. By mid-December, morning yp returned
to values very near afternoon yp and were only slightly
lower than before the onset of subfreezing nights. A preliminary model is proposed which interprets the qualitative interaction between air and soil temperatures, soil and plant
water potentials, and leaf conductance during seasonal stomatal closure in fall.
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