A study by researchers at Ohio State University found that the increased heat and low water conditions caused by climate change weaken the resistance of pine trees to disease by weakening their capability of defending themselves while fungi in their tissues become more aggressive, according to Emily Caldwell of Ohio State News.
The unprecedented study, published in the peer-reviewed journal Frontiers in Forests and Global Change last month, examines metabolic gene expression in both pine trees and the organisms attacking them under normal conditions and under conditions affected by climate change, Caldwell added, noting that the research could help explain how global warming renders trees more vulnerable to diseases.
The researchers studied the effects of climate change on Austrian pine trees after they were infected by two related fungi, Diplodia sapinea and Diplodia scrobiculata, both known to be deadly to these trees.
“We decided to study the effects of the combined stresses of higher temperatures and lower water availability because that’s what trees will experience in the future,” said Enrico Bonello, senior author of the study and professor of molecular and chemical ecology of trees at OSU's Department of Plant Pathology.
“Within three days of infection under climate-change conditions, the tree was pulled in two different directions: It was deprived of carbon by both reduced photosynthesis and enhanced acquisition of the carbon by the fungi. When we’re talking about carbon, we’re talking about sugars, food and reserves for all other metabolic processes in the trees, including growth and defense.”
“Essentially, climate change conditions led the host to starvation, which is compounded by the fact that the fungi became more aggressive, grew faster and killed more host tissue faster,”Enrico Bonello, senior author, professor of molecular and chemical ecology of trees, Department of Plant Pathology, Ohio State University
The researchers subjected one group of 3-year-old autrian pines to daily temperatures between 59 and 82.4 degrees Fahrenheit as the control, and subjected another group to daily temperatures between 68 and 91.4 degrees Fahrenheit to simulate climate change, reducing the amount of water in the atmosphere. Then, the researchers exposed the trees to one of two strains of the fungus.
Three days after the trees were infected, the researchers collected tissues from the plants and the pathogens for an RNA sequencing analysis to find changes in the patterns of gene expression in the trees and the fungi.
The team found that the trees' ability to perform photosynthesis was diminished by the climate change conditions, so they had fewer resources to use to defend against disease, according to Caldwell. Furthermore, although D. scrobiculata is typically less aggressive than D. sapinea, both strains increased their use of carbon and the distinction between their levels of aggressiveness disappeared under climate change conditions.
“Essentially, climate change conditions led the host to starvation, which is compounded by the fact that the fungi became more aggressive, grew faster and killed more host tissue faster,” explained Bonello. “These were early responses, but it gives us an idea of what’s happening in the system.”
Caldwell noted that although the study only accounts for one species of tree and one type of pathogen, the findings could help scientists gauge how much damage climate change might cause to trees, in general, which she noted are one of Earth's primary carbon sinks.