LOW ROOT TEMPERATURES AND GROWTH OF EUCALYPTS 
69 
would have included a greater number of parent 
trees. 
A selection of uniformly large seeds was ger¬ 
minated on moist plugs of sterile rock fibre. E. 
delegatensis was sown after 6 weeks stratifi¬ 
cation at 4°C. Because of greater growth rate of 
seedlings, seeds of all other species were sown 
one month later. Five seeds were sown in each 
plug. After germination each plug was placed on 
the top of a 250 mm length of 60 mm diameter 
PVC pipe filled with clean river sand. The seed¬ 
lings were kept moist in a shade house by spray 
irrigation and fertilized every third day with 10 
mL of water and 10 mL of Duralite HysoL a 
complete hydroponic nutrient solution. Once es¬ 
tablished, the seedlings were thinned to leave 
one plant within each growth tube. 
After 115 days from the first sowing, the 
plants were transferred to an empty glasshouse 
where they were temporarily stored on the floor. 
After measuring plant height, ten individuals of 
each provenance were randomly chosen for in¬ 
itial dry weight and root length determination. 
At this stage the E. nitens seedlings developed a 
light infection of powdery mildew. All plants 
were elevated on benches and given two appli¬ 
cations of TILT (Ciba-Geigy), a wide spectrum 
Triazole derivative systemic fungicide at a five 
day interval. Within ten days there was no evi¬ 
dence of active infection. The plants were given 
a further 20 days to recover and acclimatise to 
the glasshouse before the cool root treatment 
was applied. During this period all seedlings 
were showing healthy and apparently unaffected 
new growth. The E. delegatensis seedlings were 
therefore 145 days old at the commencement of 
the experiment. 
Two root temperatures were replicated three 
times, in six forced air coolers. Mean warm root 
temperatures were maintained between 8.5°C 
and 10.5°C while mean cool root temperatures 
were maintained between 4.5°C and 6.5°C. Tem¬ 
peratures were measured using mercury ther¬ 
mometers inserted to a depth of 75 mm at both 
ends of the cooler. The treatments were arranged 
down the centre of the glasshouse so that the dif¬ 
ferent root temperatures were adjacent. Five 
plants of each of seven provenances were allo¬ 
cated at random to each of the six coolers. The 
plants were evenly distributed with their centres 
110 mm apart. 
The growth tubes were suspended through a 
false lid so that the roots in each tube were sur¬ 
rounded by fan-circulated air at controlled tem¬ 
perature, while the aerial parts of each plant 
were exposed to the ambient temperature of the 
glasshouse. A small temperature gradient of ap¬ 
proximately PC existed across each cooler, and 
small differences in the operation of thermostats 
meant that the regulation of root temperature 
differed slightly between coolers. To compen¬ 
sate, lids were moved between coolers and 
turned once through 180° within each cooler so 
that, as far as possible, all plants experienced an 
equivalent root and shoot environment. 
Temperature control in the coolers was 
adequate to ensure that clear differences existed 
between treatments and that similar tempera¬ 
tures were maintained between replicates (Table 
2). Some difficulties were experienced in adjust¬ 
ing the thermostat in cooler 1 and the cooler was 
replaced after 16 days. Cooler 6 failed over a 
weekend and was replaced the following Wed¬ 
nesday. Typically, temperature fluctuates in the 
upper soil horizons both diurnally and annually, 
and lags behind air temperature. Experimentally 
maintained constant temperatures do not mimic 
most natural situations, although they may be 
more typical of soils protected by dense, rain¬ 
forest vegetation. Watson (1980) considered 
that soils above 400 m elevation of the Great 
Dividing Range of Victoria are likely to have a 
mean annual temperature between 8°C and 
15°C. On Errinundra Plateau at mid morning in 
mid November, soil temperatures of 7-8°C were 
obtained using a mercury thermometer at 130 
mm depth, beneath dense rainforest vegetation. 
It is therefore conceivable that the experimental 
Treatment 
Temp (°Q 
Cooler 
May/June (°C) 
July (°C) 
Period 
Aug/Sept (°C) 
May/Sept (°C) 
10°C 
1 
9.8-12.5 
8.6-9.5 
8.9-9.6 
9.1-10.5 
3 
9.6-10.7 
8.2-9.4 
8.5-9.6 
8.8-9.9 
5 
9.4-11.8 
8.5-9.4 
8.8-9.9 
8.9-10.4 
5°C 
2 
4.8-6.3 
4.5-6.7 
4.8-6.1 
4.7-6.4 
4 
5.1-6.1 
4.4-5.0 
5.0-6.0 
4.8-5.7 
6 
6.2-7.4 
4.6-5.5 
4.4-5.8 
5.1-6.2 
Table 2. Mean minimum and maximum soil temperature in each cooler. 
