Growth and Developmental Responses of Perennial Ryegrass Grown at Constant Temperature. II. Influence of Light and Temperature on Leaf, Tiller and Root Appearance

Abstract

Spaced plants of perennial ryegrass (Lolium perenne L. cv. Grasslands Ruanui) were grown in nutrient solution under six levels of irradiance at six temperatures (7-33°C). Response curves to light and temperature of leaf, tiller and root appearance rates were determined during the exponential growth phase. Appearance rate responses showed saturation-type kinetics with irradiance, the shape of the response curve being temperature dependent. Light-saturated appearance rates increased with temperature over the 7-17°C range, but were independent of temperature above 20°C. No apparent optimum temperature was found for leaf appearance, root appearance or tillering in the 7-33°C range. The ratios for both tillering/leaf appearance and root appearance/leaf appearance (light-saturated) were notable for their insensitivity to temperature. The results indicate that light and temperature determined the rate of leaf appearance through effects on the rate of assimilate supply and utilization at the stem apex. Leaf appearance rates determined the potential rates for tiller and root axis production through determining the sites available. Low irradiance combined with high temperature reduced tillering below the potential but did not reduce root production.