Effect of low root temperature on net photosynthesis, stomatal conductance and carbohydrate concentration in Engelmann spruce (Picea engelmannii Parry ex Engelm.) seedlings.

The effect of low root temperature on net photosynthesis, stomatal conductance and carbohydrate concentration in potted Engelmann spruce (Picea engelmannii Parry ex Engelm.) seedlings was examined under controlled growth-chamber conditions. Root temperature had no effect on net photosynthesis between 10 and 20 degrees C, however, conductance and photosynthesis declined sharply below 8 degrees C. Net photosynthesis and stomatal conductance decreased to 50 and 34% of the initial values after 7 days at a root temperature of 0.7 degrees C. Low root temperature also caused a decrease in photosynthetic utilization of internal CO(2), carboxylation efficiency and apparent quantum yield, and it was concluded that the decrease in photosynthetic rate was caused primarily by nonstomatal limitations. Root chilling caused a small increase in starch content in needles and stems and induced the hydrolysis of starch to glucose in roots. The increase in glucose concentration may enable continued root growth at low temperatures.