Abstract
(1) Research Highlights: Thermal damage to cambium cells of Eucalyptus held in vitro was recorded at sublethal temperatures (40 °C–50 °C) when the duration of exposure extends beyond 2.5 min up to 5 min. (2) Background and Objectives: During a forest fire, heat can be transferred through tree bark potentially impacting viability of vascular cambium cells and the perennial growth of the tree. With the increased temperature of the cambium, cells are known to lose viability at temperatures exceeding 60 °C. However, it is possible that extended exposure to temperatures below 60 °C may also impair cell viability. This study aimed to identify the effect of the temperature and exposure time interaction on the cambium cell viability of Eucalyptus, a genus widely distributed in natural forests and commercial plantations globally. (3) Methods: Excised cambium-phloem tissue sections from three Eucalyptus species (Messmate–E. obliqua L’Hér., Narrow-leaf peppermint–E. radiata Sieber ex DC. and Swamp gum–E. ovata Labill.) were exposed in vitro to a series of temperature–time treatments (40 °C, 50 °C, 60 °C, 70 °C for 1 min, 2.5 min, and 5 min) and tested for cell viability using a tetrazolium reduction method. (4) Results: Cell viability of cambium cells decreased with increased temperature and exposure times for all three Eucalyptus species. Longer exposure to sublethal temperatures of 40 °C to 50 °C showed statistically similar results to shorter exposure to lethal temperatures (>50 °C). (5) Conclusions: Longer exposure to sublethal temperatures (40 °C–50 °C) caused irreversible thermal damage to cambium cells of Eucalyptus when tested in vitro, further refining our understanding of raised temperature on cell viability.
Highlights
Vascular cambium regulates the secondary growth of a tree by producing secondary xylem and phloem [1,2]
This study aimed to identify the effect of the temperature and exposure time interaction on the cambium cell viability of Eucalyptus, a genus widely distributed in natural forests and commercial plantations globally
The traditional methodology for determining cell death following heat exposure has been to define a critical temperature at which cells lose viability, which in most of the previous studies has been demonstrated at 60 ◦C [9,10,11,12], including for Eucalyptus species [13]
Summary
Vascular cambium regulates the secondary growth of a tree by producing secondary xylem and phloem [1,2]. Due to some combination of temperature and duration of heat exposure, irreversible thermal damage occurs, ceasing the production of xylem and phloem cells by cambium and potentially leading to tree death [7,8]. The traditional methodology for determining cell death following heat exposure has been to define a critical temperature at which cells lose viability, which in most of the previous studies has been demonstrated at 60 ◦C [9,10,11,12], including for Eucalyptus species [13]. To develop a better understanding of heat impacts on cambium cell viability, it is essential to describe the interaction between temperature and time of exposure to raised temperature. For the purpose of this study, 40 ◦C to 50 ◦C was considered the sublethal temperature range and temperatures above 50 ◦C were considered as lethal for cambium-phloem tissue samples
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