© 1991 Heron Publishing—Victoria, Canada
New root growth of Douglas-fir seedlings at low carbon dioxide concentration
R. van den Driessche
Research Laboratory, Ministry of Forests, 1320 Glyn Road, Victoria, British Columbia, Canada VSZ 3A6 / Received August 13, 1990
Summary
New root growth of conifer nursery seedlings is dependent on light, but whether this is necessary only for photosynthesis,
or also has some other root growth promoting effect is unknown. This question was investigated using one-year-old Douglas-fir
(Pseudotsuga menziesii (Mirb.) Franco) seedlings grown at two nurseries from the same seed lot and taken from cold storage in March and April. New
root production was examined in two 10-day root growth capacity (RGC) experiments. Seedlings were subjected to one of four
treatments: (1) control, (2) exclusion of light, (3) low CO2 concentration, and (4) girdling to separate the phloem connection between shoot and root. Shoots were enclosed in Plexiglas
cuvettes and supplied with scrubbed air to reduce the CO2 concentration to 11 to 22 μl l–1 in the light. The closed system used in Experiment 1 was opened to the atmosphere briefly each day to restore O2 to ambient, but this was unnecessary for the open system used in Experiment 2. In Experiment 1, new root production was affected
by treatments in the order: control > low CO2 concentration > dark > girdling. Greater new root production in the low CO2 treatment compared with the dark treatment was attributed to brief increases in CO2 to ambient concentrations when O2 was restored each day. In Experiment 2, new root production at the low CO2 concentration in the light was essentially the same as in darkness, but only 17% of the control value. Thus light appeared
to play no part in new root production other than permitting photosynthesis. Limited production of new roots occurred in the
absence of photosynthesis, which was further reduced by girdling, presumably because, after girdling, only root system reserves
could be used.
