As global temperatures rise, research has revealed that some tropical trees have developed effective strategies to cool their leaves and survive in increasingly hot environments. A study conducted by researchers, including Kali Middleby from James Cook University, examined how certain tree species adapt to heat stress, potentially offering them a competitive edge in a warming climate.
Tropical forests are crucial for biodiversity and play a significant role in carbon dioxide absorption. Yet, rising temperatures and climate variability pose serious threats to many tree species. The study focused on understanding how specific trees, particularly Darlingia darlingiana (silky oak), Elaeocarpus grandis (blue quandong), and Cardwellia sublimis (bull oak), manage to regulate their leaf temperatures to mitigate the effects of heat.
Mechanisms of Leaf Cooling
In hotter climates, trees can employ various mechanisms to prevent heat damage. One method involves the evaporation of water through tiny pores known as stomata, which helps cool the leaves. Another approach includes the development of narrower, smaller leaves that shed heat more effectively than larger leaves. This is because wind can flow closer to the leaf surface, disrupting the insulating layer of still air. Additionally, the orientation of leaves can change to minimize sun exposure.
The research team sampled trees from 16 forest sites across the Wet Tropics of Queensland, gathering data on leaf characteristics that influence temperature. Using a giant slingshot, they collected branches from high in the canopy, measuring factors such as leaf width, thickness, chemical composition, and color reflectivity. These measurements were entered into a computer model to assess how temperature differences varied across different habitats.
Results indicated that both silky oak and blue quandong demonstrated notable self-cooling abilities in hotter environments. These species increased stomatal activity and had smaller leaves, allowing them to better manage leaf temperatures.
Investigating Genetic Adaptation
To determine if the ability to cope with heat was a result of genetic adaptation, the researchers analyzed the DNA of the three species. They sought to find genetic markers linked to the specific climates where the trees grew. Findings revealed that all three species exhibited genetic responses influenced by both temperature and rainfall, indicating evolutionary adaptations shaped by climate history.
Further experiments were conducted using blue quandong seedlings from various populations. The seedlings were subjected to different temperature conditions in a glasshouse setting, simulating the current environments of uplands and lowlands. The results showed that seedlings maintained the same variation in leaf-to-air temperature differences observed in the field, regardless of the environment in which they were grown. This suggests a genetic basis for the ability of some tree populations to keep their leaves cooler.
The implications of these findings are significant for conservation efforts. Understanding which species can adapt to rising temperatures is essential for guiding rainforest restoration initiatives in a changing climate.
As heatwaves and droughts become more frequent, the survival of tree species that lack effective cooling strategies may be at risk. Trees unable to manage their leaf temperatures could face increased tissue damage, reduced growth, or even local extinction. The study highlights the importance of ongoing research into how tropical trees adapt to climate change, which is critical for their preservation and the overall health of rainforest ecosystems.
Funding for this research was provided by James Cook University, the Holsworth Wildlife Research Endowment, and the Skyrail Rainforest Foundation.
