Seedlings and one-year-old trees of Douglas-fir (Pseyidotsuga menziesii) were grown in chambers with atmospheres maintained at 0.03% to 5.0% CO₂ (by volume). Carbon dioxide treatments were given
in conjunction with daylengths of 8 or 16 hours and light intensities which varied from 3.4 mW cm⁻² to 7.2 mW cm⁻² (400 - 700 nm). The
duration of treatment varied from 30 days to 12 weeks.
When plants were treated with 0.1% CO₂ both seedlings and trees showed enhanced growth, as demonstrated by increases in dry weight and internodal elongation. CO₂ enrichment caused growth enhancement to a degree that other factors became limiting, e.g., irradiance. Carbon dioxide concentrations of 1.0% CO₂ and
higher generally inhibited growth, as shown by decreases in internodal elongation, dry weight, and leaf area. Plants grown under high carbon dioxide levels ceased active growth and exhibited increased budset and frost hardiness. High CO2 levels appeared to override photoperiodic control of budset by promoting budset even under warm temperatures and long days. CO₂-induced frost hardiness appears to require an active metabolism, indicating that the mode of CO2 action is through increased production of cryoprotectents, such as amino acids and sugars.
In some cases, carbon dioxide may substitute in part for the light requirements of photosynthesis when light is limiting. Thus, an increase in daylength may reduce the level of CO₂ required for a particular effect, e.g., the required CO₂ levels for inducing frost hardiness are reduced from 1.0% to 0.1% CO₂ if long days are
provided.
Plants which have been grown under normal air (0.03% CO₂) have higher photosynthetic rates than enriched plants when all plants are measured in normal air; the concentration under which plants are measured appears to have more effect on photosynthetic rates than the CO₂ concentration under which the plants are grown. Under long days and high CO₂ (1.0% CO₂ and higher), plants show reduced diffusion resistance, but the beneficial effects on photosynthesis
due to potential reduction of CO₂ diffusion resistance are lost as a result of increased rates of respiration under high CO₂. Thus, the enhancement of growth under 0.1% CO₂ and the inhibition of growth under 1.0% CO₂, appear to be mostly related to differences in respiration under the various carbon dioxide treatments. All effects of carbon dioxide may not be due to gas exchange characteristics alone, but may result from changes in levels of growth inhibitors, such as abscisic acid.
The effects of CO₂ on growth and development were examined over a range of CO₂ concentrations. Over the entire range CO₂ was found to effect both growth and development and the processes underlying growth and development. / Science, Faculty of / Botany, Department of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/22193 |
| Date | January 1979 |
| Creators | Leadem, Carole Louise Scheuplein |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
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