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We sought to determine the individual contributions of ambient root and shoot temperatures to rate of plant development, dry matter accumulation, and root/shoot ratio. Subterranean clover (Trifolium subterraneum L., subsp. yaminnicum Katznelson and Morley)' plants were grown from seed to the 7- to 10- leaf stage in sand-nutrient culture. Combinations of 10 and 20 C were used in the following basic chronological sequence: (i) plants were grown at 20 C from seed to the two-leaf stage; (ii) root, shoot, or overall temperature was then lowered to 10 C and growth was allowed to progress until the five-leaf stage; and (iii) temperature was returned to 20 C and growth was continued to the 7- to 10- leaf stage.
Growth was expressed as a regression of trifoliolate leaf number on days accumulated (y = bx + a) within each of the three growth intervals. For intervals (i) and (iii), b = 0.32 and 0.44, respectively. For (ii), b = 0.20 (root temp. 10 C), and 0.15 (overall temp. 10 C). Correlations (rxy) = 0.99 in all instances. Plant weights were more closely related to final stage of plant development than to temperature treatment. Root/shoot ratios averaged 0.44. Shoot ambient temperature appeared to be less important than root ambient temperature as a determinant of growth rate.
Key Words: Root/shoot ratio Controlled environment Trifolium subterraneum L. subsp. yaminnicum Katznelson and Morley
2 Specialist, Associate Professor, and Staff Research Associate, respectively, Department of Agronomy and Range Science, Agricultural Experiment Station, University of California, Davis.
Received for publication January 24, 1972.
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