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Annals of Botany 37: 519-537, 1973
© 1973 Annals of Botany Company

RESEARCH-ARTICLE

The Effects of Light Intensity and External Potassium Level on Root/Shoot Ratio and Rates of Potassium Uptake in Perennial Ryegrass (Lolium perenne L.)

R. HUNT and JUDITH A. BURNETT

Department of Botany, The University Bristol, BS8 1UG

Received: 3 July 1972   

Loliun perenne L. (cv.S. 23) was grown on vermiculite in winter in a heated greenhouse for 8 weeks under factorial combinations of two potassium regimes (nominally 6 parts/106 and 156 parts/106 in Hewitt's solution) and three densities of artificially supplemented visible radiation flux (36.1, 7.3, and 2.2 W m–2). Growth and potassium uptake were studied through the calculation of various growth functions from fitted curves.

There was little effect of potassium treatment but the experimental material responded markedly to light. Leaf-area ratio in the three treatments showed extreme plasticity in increasing from 2–3 x 10–2 through 6 x 10–2 to 8–9 x 10–2 m2 g–1 as light intensity decreased. Corresponding decreases in unit leaf rate, however, caused over-all reductions in relative growth rate.

Specific absorption rates for potassium (AK, dry-weight basis) were strongly reduced at the lower light intensities but also displayed complex ontogenetic drifts. Values of the allometric constant, k (the ratio of root and shoot relative growth rates), decreased from c. 0.7 at 36.1 W m–2 through c. 0.3 at 7.3 W m–2 to a value not significantly different from zero (P < 0.05) at 2.2 W m–2.

In material grown under the two higher light intensities a constant inverse relationship was found between the mass ratio of root and shoot and the corresponding activity ratio. The results conform to this model: Mass ratio = –0.001+45.0 (1/activity ratio) where activity ratio is expressed as specific absorption rate for potassium (in µg g root–1 h–1)/unit shoot rate (rate of increase of whole-plant dry weight per unit shoot dry weight, in mg g shoot–1 h–1). The implications of this relationship are discussed.


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