Arboriculture & Urban Forestry 47(4): July 2021 in dormant bud development has been less researched (Meier et al. 2012; Clarke et al. 2013). There is a long and extensive literature on the effects of high and low temperatures on leaves, seeds, fruits, pollen, and whole plants, but there are few reports on the effects of high temperatures on roots (Levitt 1972; Precht et al. 1973; Hood et al. 2018). Root tissues cease functioning in nutrient absorption and water uptake at about 40 °C (Precht et al. 1973), and it is generally assumed that root cells and tissues are killed over the range of 50 to 60 °C that kills plant cytoplasm (Levitt 1972; Busse et al. 2005; Bär et al. 2019). One of the reasons why there is little informa- tion on lethal root temperatures is that, under natural circumstances, temperatures are unlikely to be high enough to do damage. Soil is such a good insulator that at depths of 25 mm to 50 mm, soil temperature varies little, depending on soil type, organic matter, and moisture content, even in forest fires (Beadle 1981; Preisler et al. 2000; Busse et al. 2005). A ques- tion that arises in relation to shoot mortality is the role played by a tree’s root system in the production and successful growth of shoots. This paper investigates the responses of E. obliqua seedlings subjected to two forms of stress, both of which left the root system intact but which caused dif- ferent levels of damage to the aboveground parts of the trees. The first experiment involved exposure to temperatures ranging from 40 to 100 °C for different durations. While the temperatures are not as high as those experienced in a forest fire, the stresses imposed can inform plant responses to stress such as fire. It was hypothesised that: 1. apart from affecting aboveground parts of the plant, stress at this level would affect roots; 2. there would be an interaction between root growth and the initiation of new lignotuberous or epicormic shoots in plants that recovered from the stress imposed; 3. because root tissues were not directly damaged by the treatments, root growth, if disrupted by the level of stress imposed, would resume prior to shoot production, and that if there was no resumption of root growth, there would be no shoot growth. High temperature stress produces chemicals such as phaeophorbide that may inhibit shoot development (Kim et al. 2018; Kuai et al. 2018; Aubry et al. 2020). Heated seedlings were subjected to the removal 135 (decapitation) of damaged tissues either immediately or a week (delayed) after the heat treatment. It was hypothesised that: 4. after heat stress, plant responses and/or chemicals produced as a result of the stress could inhibit or delay recovery, and that immediate removal of damaged tissues might result in earlier shoot initiation. The second experiment involved “parallel” decapita- tion of seedlings, where the decapitations “paralleled” the amount of stem tissue and number of leaves that were left undamaged after heat treatments. It was hypothesised that: 5. an element of the response to high temperatures was due to the killing or removal of stem tissue and foliage. The third experiment, which left different numbers of intact leaves on seedlings, was undertaken to examine the hypothesis that: 6. the more healthy foliage a seedling retained after decapitation or heat stress, the more likely it was to produce epicormic or lignotuberous shoots that survived and grew. The nodal positions and mortality of shoots produced and the rates of seedling growth were recorded after treatment. The relationships between epicormic and lignotuberous bud development, shoot mortality, root tip growth, and the presence of intact leaves were investigated. MATERIALS AND METHODS E. obliqua seedlings were grown from seed (Daylesford, Victoria source) for 8 months under ideal greenhouse conditions, where the temperature within the green- house was held at 23 ± 6 °C with a daily temperature variation of ± 3 °C. Seedlings used in experiments were approximately 300 mm high, with a stem calli- per above the lignotuberous swelling of 3 mm to 4 mm. Trees were grown in specially designed containers so that root systems could be inspected daily to deter- mine whether the root tips were healthy, and selected root tips were monitored for growth and to determine if and when they had resumed growth after treatment. Trees were grown in a pasteurised, soil-based medium so that soil insulation properties were retained. The containers were made from PVC pipe with a diameter of 70 mm cut into 200-mm lengths with a smooth inner surface (Figure 1). At the base, 4 lugs were cut ©2021 International Society of Arboriculture
July 2021
| Title Name |
Pages |
Delete |
Url |
| Empty |
Ai generated response may be inaccurate.
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success.
Downloading PDF
Generating your PDF, please wait...
This process might take longer please wait
