BIOMASS PARTITIONING IN CORYMBIA CITRIODORA, EUCALYPTUS CLOEZIANA AND E. DUNNII STOCK PLANTS IN RESPONSE TO TEMPERATURE

Production of subtropical eucalypt cuttings is limited by low temperatures but nothing is known about the effects of temperature variation on biomass partitioning within eucalypt stock plants. This study determined whether changing the temperature from 28/23 °C (day/night) to 18/13, 23/18 or 33/28 °C affected the distribution of biomass among the roots, pruned hedge and cuttings of Corymbia citriodora, Eucalyptus cloeziana and E. dunnii stock plants. Root/shoot ratio was significantly higher at 18/13 °C than at 33/28 °C, with the roots of the three respective species comprising 36, 50 and 37% of total plant biomass at 18/13 °C but only 24, 27 and 18% of total plant biomass at 33/28 °C. The responses to low temperature in the Eucalyptus species were highly unusual since root/shoot ratio was elevated at 18/13 °C because of an increase in root mass. Subtropical eucalypt stock plants divert biomass production from their shoots to their roots under conditions of low temperature. Thus, sustained cutting production may require that nurseries upgrade the climatic protection for stock plants during winter conditions.