Thick-leaved tropical crops can thrive as CO2 rises, which might be good for the local weather – Watts Up With That?
WASHINGTON UNIVERSITY
Research news
PICTURE: THIS PHOTO SHOWS THE 2007 RAINFOREST ON PANAMAS BARRO COLORADO ISLAND. THE ISLAND HAS A RESEARCH STATION FOR THE STUDY OF TROPICAL PLANTS AND ECOSYSTEMS THAT THE DATA FOR THE… View more CREDIT: SCOTT ABLEMAN / FLICKR
How plants will develop when carbon dioxide levels continue to rise is a delicate problem that researchers in the tropics say is particularly annoying. Some aspects of plant survival may become easier, some parts more difficult, and there will be species winners and losers. The resulting shifts in vegetation will help determine the future direction of climate change.
To investigate this question, a study conducted by the University of Washington looked at how tropical forests, which absorb large amounts of carbon dioxide, might adapt as CO2 continued to rise. Their results show that multiple changes in the leaves of plants and competition between species could preserve the ability of these ecosystems to absorb carbon dioxide from the atmosphere. The resulting paper was published in Global Biogeochemical Cycles on January 16.
“Our results suggest that plants with some types of responses, such as leaf thickening, ultimately grow better than their competitors in tropical forests,” said senior author Abigail Swann, professor of atmospheric science and biology at UW . “If these better-growing plants were more abundant in the forest, the overall rates of water and carbon exchange could stay closer to what they are now.”
A previous study by Swann’s group showed that tropical plant leaves get thicker as CO2 increases, which would make climate change worse, as thicker leaves could also be smaller. Plants would then capture less sunlight for photosynthesis, absorb less carbon dioxide from the air and give off less water vapor, which makes warming from climate change worse.
The new work expands the scope of this question to include competition between plant species and the ratio of carbon and nitrogen in their leaves. A higher carbon dioxide in the atmosphere makes photosynthesis easier for plants. However, if nitrogen cannot keep up, the plant will be less efficient at generating energy.
“Although this is being observed, the verdict is still unclear why exactly plants with high CO2 emissions grow thicker leaves,” said Swann. The new model study suggests an explanation: “Thicker leaves can concentrate the nitrogen so that the photosynthesis rates per leaf area are high.”
The authors ran simulations for Barro Colorado Island, a forested tropical island in Panama on which the model had been well tested against soil conditions. The simulations included one or two species of evergreen tropical deciduous trees such as wild cashew and Ecuadorian laurel. The trees were programmed in such a way that they react differently to the higher carbon dioxide and can compete with one another for space.
Trees programmed to have more carbon in their leaves relative to nitrogen became less efficient at photosynthesis, making them easier to grow, and emitting less water vapor, keeping the trees cool. But tree species whose leaves were also thickened were better at absorbing carbon and producing water vapor, helping them grow tall and staying cool, and also outperform their neighbors.
“Our work suggests that relocating the plants growing in the forest may result in fewer dire consequences of higher CO2 emissions than other studies have suggested,” said Swann. “There’s a lot we still don’t know about how plants respond to climate change. This work provides some good guesses about which plants will grow best in future tropical forests that we can test with further observations.”
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This research was funded by the National Science Foundation and the US Department of Energy. The main author was the UW doctoral student Marlies Kovenock; Co-authors are Charles Koven and Ryan Knox of the Lawrence Berkeley National Laboratory; and Rosie Fisher at the National Center for Atmospheric Research.
From EurekAlert!
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