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Effect of Gaseous Composition of Root Environment upon Root Development and Growth of Nicotiana tabacum L.¹

Tobacco gaseous treatments The extent of root and shoot injury of tobacco plants exposed to various gaseous treatments (O₂, CO₂, N₂) in the root environment was determined by microscopic examination of roots, stem diameter changes, and shoot measurements. An attempt was also made to determine the relative importance of O₂ deficiency and CO₂ excess in causing the observed injury. The plants were grown in an environmental control chamber with roots in an intermittent solution mist in airtight chambers.

Oxygen levels of 2.5%, with and without 18.5% CO₂, the remainder being N₂, caused no apparent reduction in root or shoot growth. One percent O₂ plus 99% N₂ treatments for 24 or 48 hours reduced the rate of growth during treatment; but the plants resumed a normal rate of growth during recovery. One percent O₂ plus 20% CO₂ plus 79% N₂ treatments for 24 or 48 hours caused death of several root tips, chlorosis of the lower leaves, necrotic areas on some other leaves, and considerable reduction in the rate of growth during treatment. Treatments with pure N₂ for 12 hours caused growth to cease for 60 hours. Treatments with pure N₂ for 24 hours resulted in death of the root system within 4 days. Treatments with 21% CO₂ for 24 hours killed the plants more quickly than did pure N₂.

Key Words: drainage • aeration • oxygen deficiency • excessive carbon dioxide

² Research Plant Physiologist, SWCRD, ARS, USDA, and Professor of Biological and Agricultural Engineering, North Carolina State University, Raleigh, N. C. 27607.

Received for publication December 21, 1967.