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Growth of Young Tobacco Plants as Affected by Carbon Dioxide and Nutrient Variables¹

Tobacco (Nicotiana tabacum L.), essentially a nursery plant during seedling growth, is grown in a protected plant bed until it attains the size to be transplanted into the field. Enchancement of growth rates during seedling culture would have advantages in production of tobacco seedlings, as well as bedding plants. Enrichment of atmospheric CO₂ is a generally recognized technique of increasing growth rates. Experiments were conducted in controlled-environment chambers to evaluate the immediate effects of CO₂ enrichment on seedling growth of tobacco, the carryover effects to post-transplant growth, and nutritional requirements tor maximum response to CO₂ enrichment.

Tobacco seedlings were grown at two rates of nutrient application in atmospheres containing either ambient (400 ppm) or enriched (1,000 ppm) CO₂ levels. At time of transplanting, half of the plants from each CO₂ environment were reciprocally exchanged. During seedling culture, Relative Growth Rate (RGR) was enhanced C0₂ enrichment but was depressed by the higher nutrient application rate. The RGR to CO₂ enrichment was reversed during post-transplant culture. For either CO₂ environment, RGR during seedling growth was nearly three-told RGR during post-transplant culture. The reduction in RGR with CO₂ enrichment occurred for both a 9-hour and a 15-hour light period of 450 hectolux intensity. The lower RGR for CO₂ enrichment during post-transplant culture was associated with increased starch in leaf tissues. These data support the hypothesis that, although growth response may temporarily be enhanced by CO₂ enrichment, it must decline to a level similar to that of plants raised under ambient CO₂.

Key Words: Growth analysis • Nitrate N • Relative growth rate • Starch

² Research associate (formerly, graduate research assistant) and assistant professor, Dep. of Soil Science; associate professor and professor, Dep. of Botany; North Carolina State Univ., Raleigh, NC 276O7.

Received for publication January 22, 1975.