During drought, Panama's rainforests have a “rescue strategy” to adapt to water shortages by sending their roots deeper underground, a new study has found. But scientists warn this may not be enough to save them from the ravages of climate change.
Rainforests are home to more than half of the world's terrestrial biodiversity And store large amounts of global carbon. Lots of this carbon is held in their roots underground. However, climate change rising temperatures in these forests and there is this is expected to lead to severe drought.
Scientists erected transparent roof structures over the plots, which prevented 50–70% of precipitation from reaching the forest floor. According to a co-author of the study, the structures “look like partial greenhouse roofs.” Daniela Cusackan ecosystem ecologist at Colorado State University, told Live Science. She was has been leading the PARCHED experiment since 2015.. The researchers also dug trenches around the plots and lined them with thick plastic to prevent roots from accessing water from outside the plots.
Researchers used three methods to find out what was happening to tree roots.
They collected soil samples four times a year for five years. The cores extended approximately 8 inches (20 centimeters) below the surface. The researchers also had root traps, which are mesh posts filled with soil. Every three months we checked how many roots had grown into these columns.
The third method was to use small cameras to observe root growth. When the PARCHED experiment was set up, the researchers buried acrylic tubes about 4 feet (1.2 meters) into the ground. These tubes are spaced at regular intervals with cameras looking into the soil.
All four forests, although different from each other, showed similar responses to the slowly drying environment.
Chronic drying significantly reduced the number of fine surface roots, reducing water and nutrient availability, but trees had a number of strategies to survive chronic drought.
“Trees compensated for the death of surface roots by sending fine roots deep into the soil, presumably to absorb moisture,” Cusack said.
“This root growth is not enough to compensate for the loss of carbon or biomass,” she said. It's more like “a strategy to save trees to preserve their hydraulics and physiological functions.”
At the same time, surface roots were more likely to be colonized Arbuscular mycorrhizal fungi. This type fungi enter into symbiotic relationships with plants and increases the availability of water and nutrients.
The remaining shallow roots appear to attract more of these fungi, improving their access to nutrients, Cusack said.
Daniela Yaffarwho was not involved in this study but studies the roots of tropical forests in Oak Ridge National Laboratory The US welcomed the study but said more research was needed to understand how roots behave in other tropical forests.
“Although some species have long adapted to drier environments, these adaptations typically evolve over long periods of time,” she told Live Science. “The new challenge is that tropical forests, especially in regions not accustomed to such dry conditions, may experience significant changes and not have enough time to adapt.”
Species that are less able to adapt to more severe droughts could decline or disappear from the ecosystem, she said.
Cusack warned that indigenous adaptation is not a defense against climate change. “Our five-year study is quite short in terms of rainforest life,” she said. “We don't know how long the forest can withstand this kind of adaptation.”
Lead author Amanda CordeiroThe University of Minnesota researcher, who was a PhD candidate at Colorado State University at the time of the study, told Live Science that the next steps will be to assess the long-term effects of the root changes and how they will affect the overall ecosystem in terms of carbon storage and plant fitness. “For example, it is currently unclear whether increasing the depth of root production can help tropical forests withstand ongoing chronic drying over several years,” she said.
