Further observations on root-shoot equilibria in perennial ryegrass (Lolium perenne L.)

Abstract

Plants of Lolium perenne L. (cv. S. 23) were grown in a heated glasshouse. Two experiments were performed, both during early summer. One used a sand/solution rooting medium and included low-nitrogen (0.17 parts per 106) and shade (20.2 per cent illumination) treatments; the other used aerated solution culture and involved two levels of shading (20.2 and 6.1 per cent illumination), in addition to controls. In both experiments growth and rates of potassium, magnesium and calcium uptake were studied through the calculation of various growth-functions from fitted curves.Despite the effects of treatment and environment, a constant inverse relationship was found between the mass ratio of roots and shoots and their activity ratio. These new results were added to some previously published to form a combined model: mass ratio = 0.051 + 45.7 (1/activity ratio) where activity ratio is expressed as specific absorption rate for potassium (in μg K mg root-1 day-1)/unit shoot rate (rate of increase of whole-plant dry weight per unit shoot weight, mg mg-1 day-1). The implications of this relationship are discussed and a further model is put forward in which root activity is expressed in terms of the uptake of the sum of the potassium, magnesium and calcium contents of the plant. © 1975 Oxford University Press.