Influence of Genotype and Mineral Nutrition on the Distribution of Growth within Plants of Lolium perenne L. grown in Soil

Abstract

Genotypes of Lolium perenne were grown with two levels of fertilizer application. Using exponential growth-rates and parameters derived from them, the rate of growth of each genotype was partitioned into the rates of initiation of new roots and tillers, and the growth of the individual roots and tillers after initiation. The growth of the individual roots was further analysed by measuring changes in diameter and length of the main root, and the growth in the branches of the main root. The genotypes varied in their response to additional mineral nutrition. The greater the increase in the rate of shoot growth for a genotype, the greater was its increase in the rate of tiller initiation, the smaller was the increase in the size of its tillers, and the greater was the decrease in its rate of root relative to shoot growth. Within a population of genotypes growing with the same level of mineral nutrition, the greater the rate of shoot growth of a genotype, the greater was the rate of initiation of new tillers and, at a low level of mineral nutrition, the smaller the size of tillers. With a higher level of mineral nutrition, the higher the rate of tiller production, the smaller or larger was tiller size, depending upon environmental factors other than mineral nutrition. At both levels of mineral nutrition, the greater the rate of shoot growth, the smaller was the rate of root growth relative to shoot growth, due to relatively less growth taking place in the branches of the main root.