Root and shoot elongation of rhizotron-grown seedlings of Eucalyptus nitens and Eucalyptus globulus in relation to temperature

Information on the growth response of a crop plant in relation to temperatu re can be helpful in selecting genotypes to suit local environments, schedu ling favourable time of planting and forecasting growth and yield. To deter mine the effects of varying temperature on root and shoot elongation of euc alypt seedlings, elongation rates of roots and shoots were measured in rhiz otrons for two species (Eucalyptus nitens (Deane and Maiden) Maiden, and Eu calyptus globulus Labill.) at a temperature range of 5-23 degrees C. Within this range of temperatures, elongation rates of roots and shoots of both s pecies increased with an increase in temperature. Roots of E. globulus were more sensitive and shoots less sensitive to temperature than those of E. n itens. However, the threshold temperature corresponding with zero elongatio n rate predicted from the regression of elongation rate against temperature was similar for the roots (similar to 5 degrees C) and shoots (similar to 0 degrees C) of both species. Hysteresis did not appear to have a significa nt influence on root or shoot elongation of both species during warming com pared with cooling. Results are discussed highlighting the importance of th e interaction between development and growth of plant components.