Story posted June 05, 2008
Working with researchers at the University of Western Sydney and elsewhere, they are growing Eucalyptus trees in greenhouses that produce three environmental conditions: the temperature and carbon dioxide levels that scientists believe existed at the beginning of the industrial age; the current environment; and what the world might be like at the end of the 21st century, by which time carbon dioxide levels will have nearly doubled and the earth could be almost 10 degrees (Fahrenheit) warmer.
"There has been a steady increase in carbon dioxide in the atmosphere over the past 150 years," said Logan, who directs Bowdoin's biochemistry program. "Our project will help us understand how plants might respond to a higher carbon-dioxide world."
The results of their work will inform the discussion of climate change globally, but they are particularly critical to Australia, which is more vulnerable to climate shifts and the altered cycles of rainfall and drought that could accompany them. Species of Eucalyptus dominate Australian forests, and many such forests are limited by water availability. Climate change that jeopardizes Eucalyptus survival could be devastating.
"Some Australian forests exist near the edge of survival," said Logan.
Logan spent five weeks in Australia over winter break; Hricko was there for three. Some of that time was spent in the forest on an elevated platform in the canopy of mature eucalyptus trees, where Logan and Hricko measured rates of photosynthesis and water loss under natural conditions.
To do this, they enclosed single leaves in the sealed chamber of a gas exchange analyzer. A full set of readings took more than one hour and measurements were made every three hours over two 24-hour periods.
"The data collection had to be very precise," Hricko said. "We used headlamps at night; we wanted to use as little light as possible so as not to introduce any artificial conditions. The person holding the leaf turned their lamp off or turned away."
Their controlled experiments took place in six greenhouse bays, where Logan and his colleagues have planted 110 eucalypt seedlings of two species—one that is slow growing and drought tolerant, and one that grows faster and is less tolerant of drought. They control the temperature, carbon dioxide and watering regime in each bay, and compare how the trees respond with respect to growth, photosynthesis and water loss.
So far, the results have been surprising.
Logan said he expected that the higher temperature would inhibit growth because warmth often slows the rate of photosynthesis and accelerates respiration. But the opposite has been true in plants he observed over a three-month period. When plants were provided adequate water, the plants in the 10-degree-hotter environment grew 50 percent faster.
"I didn't really appreciate how well adapted eucalyptus is to warmer temperatures," he said. "You put a red maple under those conditions and you may see a different response."
In addition, the two Eucalyptus species adjusted to carbon dioxide levels differently, and their adjustments differed at the two growth temperatures.
"Our observations underscore the complexity of plant responses to climate change and the importance of studying the combined effects of climate variables, said Logan. "They could become more water-use efficient and more tolerant of drought, leaving more water available for other uses. However, that will surely be influenced by rainfall and the effects of other climate variables on the carbon dioxide-water relationship of plants. Climate change may perturb competitive interactions among forest trees that have evolved over millennia.
Hricko, whose trip was supported by the Robert Fund. said: "My days were very full, and I felt really privileged to be able to go and work there. I was nervous going into it, but I felt I was able to contribute."
In addition to contributing to the long-term research, Hricko used the data she collected in her honors thesis on "Light use in eucalyptus exposed to past, present and forecasted future atmospheric conditions."
"Carolyn worked hand in hand with us, and did a very inspiring job," Logan said. "It could be intimidating to work on a field team made up of senior scientists, all with Ph.Ds, but Carolyn was an equal partner in the effort. In some ways, involving an undergraduate in this international collaboration was an experiment, and her success paved the way for future students."
Read more about recent student biochemistry research under Logan's mentorship.