The effects of temperature and light energy on dry weight and leaf area changes in seedling plants of Lolium perenne L

Abstract

Nine identical seedling populations of Lolium perenne cv. Grasslands Ruanui were grown at different times in a controlled environment cabinet under 22, 38, and 117 watts m-2Visible radiation (16 hr day length) and at 10, 20, and 30¦C for 32 days. The proportion of the total dry matter present as roots and that of the shoot dry weight present as leaf laminae were only slightly affected by the environment. Shoot growth was dominated by leaf growth; responses to the environment of the average relative growth rate (El,) and the average leaf area growth rate RA) were similar. RW and RA were maximal at 20¦C at each light flux density and increased toward a maximum with increased radiation at each temperature. Maximum RW for seedling plants of L. perenne was about 25% per day. The net assimilation rate increased approximately linearly with increase in light flux and was scarcely affected by temperature. The leaf area ratio was greatly affected by changes in light energy, mainly owing to change in the specific leaf area. The rate of leaf appearance was accelerated by a temperature increase from 10 to 20¦C. Total tiller number was maximal at 20¦C and increased with light flux. When related to leaf number, tillering was reduced only by high temperature at low light energy. The relative changes in net assimilation rate induced by variation in light flux at 20¦C were the same as those in the net photosynthesis of a single leaf lamina. The growth of seedling ryegrass plants in the field in winter is considered to be strongly dependent on temperature and much less restricted by low light energy.