Respiration rate of male and female cones of Pinus contorta

Summary

The effect of light on the efflux of CO₂ from reproductive structures and vegetative buds of Pinus contorta (Dougl.) was measured 12 times during the life cycle of female cones and three times towards the end of the life cycle of male cones. The net efflux of CO₂ from female cones, vegetative and male cone-bearing buds decreased exponentially with increasing quantum flux density. A simple model was derived relating temperature and quantum flux density to the net CO₂ efflux from female cones. This model was used to estimate the net respiratory losses from female cones from a few weeks after pollination until the cones senesced with the light regime normally experienced at Edinburgh (56° N). It was estimated that during that period the net respiration rate of female cones was 25% less than their dark respiration rate. This model was also used to estimate the net respiratory losses from an estimated crop of female cones in two forest stands and the simulation model MAESTRO was used to estimate the CO₂ assimilated by the needles on the trees over the same days. These simulations suggest that female cones normally respire carbon equivalent to only a small proportion (<3%) of a tree's daily assimilated CO₂.