Interspecies Variation in Terpenoid Emissions from Engelmann and Sitka Spruce Seedlings

The variation in response of terpenoid emissions to light and temperature were studied for two closely related spruce species, Engelmann ( Picea engelmannii Parry ex Engelm.) and Sitka ( Picea sitchensis (Bong.) Carr.). Isoprene was the major terpenoid emitted, accounting for approximately 75 and 69 percent of the terpenoid emissions from Engelmann and Sitka spruce, respectively. However, Sitka spruce emitted isoprene at about one-fifth the rate of Engelmann spruce. Isoprene emissions increased with light and temperature in both species, but the light response was much less in the Sitka than in Engelmann spruce. Emission rates were quantified for the most consistently detected monoterpenes from both species: α-pinene, β-pinene, camphene, β-phellandrene, and myrcene. The total monoterpene emissions from Engelmann spruce were approximately four times those of Sitka spruce. In both species, monoterpene emissions increased exponentially with temperature but were not affected by increasing light. The transpiration rates for both species increased exponentially with light and temperature and they were highly correlated with terpenoid flux. Engelmann spruce emitted significantly more isoprene and monoterpenes than did Sitka spruce, showing that high isoprene emissions could be associated with high monoterpone emissions. Forest Sci. 31:132-142.