Root growth of subalpine and montane Eucalyptus seedlings at low soil temperatures

Abstract

 This study examines the effect of different soil temperatures on root growth in seedlings of Eucalyptus pauciflora Sieber ex Sprengel subsp. pauciflora and Eucalyptus nitens (Deane & Maiden) Maiden. Seedlings were grown in a glasshouse in pots containing soil. Pots were held in water baths maintained at 3, 7 or 13°C, whilst shoots were exposed to ambient glasshouse temperatures. The experiments were designed to separate direct effects of soil temperature from effects due to differences in seedling size. In the first experiment, seedlings were grown to constant height (25 cm for both species), in the second to constant time (100 days for E. pauciflora and 64 days for E. nitens) and in the third experiment seedlings were transferred between soil temperatures. The rate of growth of both species increased with increasing soil temperature. E. nitens grew faster than E. pauciflora at 7 and 13°C, but E. pauciflora grew faster than E. nitens at 3°C. The rate of browning of roots increased with decreasing soil temperature and at a faster rate in E. nitens than E. pauciflora. Root length was highly correlated to root mass within diameter and colour classes (r² > 0.7). However, brown roots were heavier than white roots. Consequently, changes in root mass did not reflect changes in root length when the proportion of brown to white root also changed. For example, at a constant height of 25 cm at 3°C, E. nitens had greater root mass but lesser root length than E. pauciflora. E. pauciflora at 3°C grew faster, and had more root length and less brown roots than E. nitens. This supports the argument that E. pauciflora is better adapted than E. nitens to survive and grow at lower soil temperatures.