The Daintree rainforest lies on the east coast of Australia in the tropical region of North Queensland. The forest is a giant mass of green and contains all kinds of ancient plant families that date back to the time of the supercontinent Gondwana.
The Daintree and other tropical rainforests, like those in the Amazon, the Congo Basin, and southeast Asia, regulate our Earth by absorbing carbon dioxide from the air and releasing oxygen through photosynthesis. Because of this, their dense, leafy canopies help control the global climate and mitigate the effects of global warming.
However, recent research has shown that rising temperatures will significantly reduce the ability of tropical rainforests to photosynthesize.
As a result, they won’t be capable of absorbing as much carbon dioxide from the atmosphere, weakening their contribution to combating global warming and intensifying climate change.
The way that plants can acclimate to different environments is an important strategy that assists them in coping with a changing world.
In warmer conditions, they can adjust their photosynthesis to perform more efficiently, allowing them to maintain or even increase their carbon uptake.
But tropical trees have a limited ability to acclimate to warming because they evolved under relatively stable conditions. They are already near the upper limit of temperatures they can withstand without experiencing harm.
To test their limits, researchers set up an experiment in the Daintree rainforest between about 50 to 100 feet tall.
They used a canopy crane to reach the treetops and installed special leaf-heater boxes to warm the leaves of mature trees from four different species.
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They cranked the temperature up by about 39 degrees Fahrenheit, or four degrees Celsius, which is a temperature rise that is expected for tropical systems by the year 2100.
The leaf-heater boxes were made using plastic takeout containers with fishing wire to hold the leaves in place. In addition, there was a heating wire to heat the leaves.
Throughout the experiment, leaf temperatures were measured, and a feedback control algorithm was applied to maintain a consistent heat.
The experiment lasted for eight months, marking it as one of the longest-running leaf-warming experiments conducted in a mature tropical forest.
The researchers compared the physiological responses of warmed leaves and non-warmed leaves to paint a picture of how tropical tree leaves might react to future climate change. They found that warming reduced photosynthesis across all species.
The rates of photosynthesis decreased by an average of 35 percent in warmed leaves compared to non-warmed ones. Two key factors were responsible for the decline.
First of all, the leaf pores, also known as stomata, became less open in the drier air surrounding the leaves. The stomata are what let carbon dioxide enter and water escape. Secondly, the warmer temperatures hindered the enzymes’ ability to fix carbon.
After eight months of warming, the trees did not adjust very much to the higher temperatures. They did not improve their photosynthesis capabilities or shift the maximum temperature at which they can tolerate.
The findings suggest that the trees are already close to their thermal limits and cannot adapt well to rising temperatures and drier conditions.
This highlights the urgent need to protect tropical rainforests and reduce carbon dioxide emissions, which contribute to global warming.
The study was published in the New Phytologist.
