The relation between lucerne shoot growth and temperature

Abstract

Two lucerne cultivars were grown in glasshouses maintained at temperatures of 15, 21, 27, and 33¦C to study the influence of temperature on regrowth after cutting; and especially to determine whether temperature affected the response from retaining basal leaves after cutting, and also the relation between the number of shoots remaining on plants and the size to which shoots grew. In one experiment plants were cut at 5 cm above crown level, and basal leaf was either removed or retained. In cv. Totana the total weight of shoots 7 days after cutting increased with each temperature increment, but by 21 days after cutting was maximal at 27¦C. Cv. Rhizoma was less responsive to temperature; maximum weights appeared to be obtained at 27' on both days. Removing basal leaves decreased shoot weight in both cultivars at all temperatures, and there was no significant interaction of cultivars or temperatures or both with defoliation. The relative effect of removing leaves was greater at lower temperatures, and greater for Rhizoma than for Totana. In two other experiments with Totana, either all shoots were permitted to regrow after cutting or only a predetermined number. When all shoots regrew, the weight attained by individual shoots was generally independent of the number of shoots, but at 33¦C the weight attained by shoots observed shortly after cutting decreased as the number increased. Where only one, two, four, or eight shoots were permitted to grow on each plant, the weight attained by individual shoots was independent of the number present at 21¦, but at 33¦ shoots were significantly larger when only one or two were retained than when four or eight were retained. These results support the concept that shoot growth is normally restricted by environmental rather than by plant factors, and that it is only when environment is conducive to high shoot growth rates immediately after cutting that there is inter-shoot competition for growth substrates.