Growth and Developmental Responses of Perennial Ryegrass Grown at Constant Temperature. I. Influence of Light and Temperature on Growth and Net Assimilation

Abstract

Perennial ryegrass (Lolium perenne L. cv. 'Grasslands Ruanui') plants were grown spaced in nutrient golution under six levels of irradiance at six constant temperatures (7-33°C) to provide growth response curves to light and temperature over a range of growth conditions. Measurements were restricted to the exponential growth phase. Plants showed saturation-type growth kinetics with irradiance but the shape of the light response curve was temperature dependent and, conversely, the shape of the temperature response curve was irradiance dependent. Growth analysis revealed that, at 7, 10, 17 and 20°C, changes in leaf area ratio compensated for changes in net assimilation rate over a range in irradiance for which growth rate was maintained near maximum. At 30 and 33°C, the compensating effect of changes in leaf area ratio was insufficient to maintain near maximum growth at intermediate irradiances. Ontogenetic drifts in specific leaf area and leaf area ratio were compensated for by changes in net assimilation, so that relative growth rate remained constant. The maximum growth at 20°C resulted from a greater partitioning of dry weight to leaf than at lower temperatures, as well as higher net assimilation than at all other temperatures.