Studies on the carbon dioxide environment for plant growth III

Effect of the carbon dioxide concentrations on the growth, heading and yield of crisp head lettuce (Lactica sativa L. var. capitata)

Abstract

Lettuce (Lactica sativa L. var. capitata, cultivar Great Lakes) was grown in gravel culture using HOAGLAND′S No 2 solution under polyvinyl plastic growth chambers to investigate the practice of CO₂ enrichment of the atmosphere on the growth.
Four chambers were employed with each at 300 (air), 900, 1, 500 and 3, 000ppm CO₂ for 8 hours daily from April 1 to May 20, 1965.
1. Difference in growth and appearance of the plants grown under the normal and the above normal levels of CO₂ were apparent within 20 days. Fresh and dry-weight yields, number of leaves and leaf area increased with increasing CO₂ concentrations, while percentage of bolting decreased. An enhancement of NAR by increasing CO₂ concentrations was observed.
2. The effect of increased CO₂ concentrations was on growth and yield were compared with outer and inner leaves of lettuce at the end of the experiment. In the inner leaves, fresh-and dry-weight yields and number of leaves increased with higher levels of CO₂, and also in the outer leaves similar effects were found in all except number of leaves.
3. The contents of chlorophyll, nitrogen, phosphorus and potassium in leaves were determined for outer and inner leaves at the end of the experiment. All the measured constituents varied with the part of plant analyzed or CO₂ concentrations treated. Chlorophyll contents in both outer and inner leaves tended to decrease with higher levels of CO₂ regardless of plant part. In the outer leaves, N, P and K contents increased with increasing CO₂ concentrations, while in the inner leaves a decrease occurred in P and K contents but N increased as CO₂ conentrations were raised.