Short-term effects of the plant growth retardant mefluidide on drought
resistance were investigated in seedlings of western red cedar (Thuja
plicata Donn), yellow cedar (Chamaecyparis nootkatensis D. Don), and
white spruce (Picea glauca (Moench) Voss). Mefluidide was applied as a
root drench at concentrations of 0, 0. 1, and 0.4 mg - L-1. Following
this, seedlings were stressed by withholding water for a period of up
to 7 days and then watering regularly thereafter. Stomatal conductanc
e of the mefluidide-treated seedlings decreased significantly and rema
ined lower than the control seedlings throughout the stress period. As
a result of the decreased conductance, shoot water potentials in mefl
uidide-treated seedlings remained higher throughout the stress period.
There was a decrease in net photosynthesis that was partially caused
by stomatal limitations, the severity of which depended upon the conce
ntration of mefluidide applied. Mefluidide treatment also resulted in
an accumulation of abscisic acid in all three species, and this may ha
ve been responsible for the effects on stomatal conductance and water
relations. In contrast, the mefluidide-treated seedlings had the highe
st rates of photosynthesis after rewatering, resulting primarily from
a promotion of stomatal opening.