INFLUENCE OF MALE AND FEMALE CONES ON NEEDLE CO2 EXCHANGE-RATES OF FIELD-GROWN PINUS-CONTORTA DOUG TREES

In autumn, needles on the parent shoot of branches of Pinus contorta Doug. bearing male cones had significantly higher photosynthetic rates compared to needles on vegetative shoots and those branches bearing female cones. There were no significant differences between the assimilation rates of needles on vegetative shoots and branches bearing female cones in any of the three sample periods (spring, summer or autumn). It was suggested that needles on branches bearing male cones had higher autumn assimilation rates because of: (1) reduced needle complement on the current year's growth and (2) presence of a developing male cone bud. Needles on branches bearing female cones had higher respiration rates than needles on vegetative branches, at all three sample times, and significantly higher respiration rates than needles on branches bearing male cones in the spring and summer sample periods. It is suggested that the higher dark respiration rates associated with branches bearing female cones were the result of the simultaneous growth and extension of both female cones and the current year's shoots.