Tropical trees in the Amazon rainforest may be more drought resistant than previously thought, according to a new study.
That’s good news, since the Amazon stores about 20 percent of all carbon in the Earth’s biomass, which helps reduce global warming by lowering the planet’s greenhouse gas levels.
“Tropical forests act as a sink that reduces global greenhouse gases. However, if those plants die and decompose, they can become a source of atmospheric carbon. Because of its sheer size, what happens in the Amazon affects the whole world,” said Santiago, who also holds an appointment at the Smithsonian Tropical Research Institute.
Santiago said studying drought in one of the wettest places on Earth might seem counter intuitive, but recent droughts, including record heat and drought during the 2015-16 El Niño, are already threatening the Amazon Rainforest. If trees die because of those droughts, the carbon they store will be released into the atmosphere, where it will further exacerbate global warming.
When plants absorb water through their roots, they use their xylem to transport water and nutrients through the plant. As less water becomes available, a plant must “suck” harder to draw water from its roots to its leaves. At some point during this struggle, air bubbles can be pulled up into the xylem causing embolisms. These embolisms block the flow of water, leading to a phenomenon called hydraulic failure. The more readily a plant or tree develops hydraulic failure, the more susceptible it is to drought.
Further experiments revealed a glimmer of hope: tropical trees have developed another way to survive during drought. A layer of live “parenchyma” cells that surrounds the xylem helps tropical trees by storing water and mediating the osmotic pressure so that water can be redistributed to where it is most needed.
Santiago said the researchers are now expanding their study to include additional tree species in Panama and Brazil.