Fire Is Changing Aspens Before They Grow
When a fire burns through an area, one of the first plants to reestablish is the aspen tree. This is because aspens reproduce clonally, meaning new saplings sprout from the underground root system of adult trees.
Even if the trees are damaged aboveground, the root system is likely to survive well enough to produce new saplings. This got researchers wondering if trees that sprouted after a fire were any different from the ones before it. So they looked at a stand of aspens that was part of a controlled burn.
"This was a rather large prescribed burn, basically was a controlled wildfire. Basically, they lit off several thousand acres where aspen was being outcompeted by coniferous forest species, pines, spruce. And whereas the aspen is much more favorable for wildlife habitat, they were interested in regenerating those aspen stands for wildlife habitat purposes," said Chris Schadt, a senior staff scientist at Oak Ridge National Laboratory and lead author on this study.
This allowed researchers to look at saplings in areas of different burn severity. Specifically, the researchers looked at the microbiome of the plants. They expected the majority of the microbes to be similar to the unburned trees because of the common root system.
"We could see definite effects of the fire severity on the soil and root-associated soil microbiomes. There was a divergence depending on fire severity. We also looked at the stems and the leaves of the plants aboveground and the roots of the plants within the ground, and we couldn't see effects there except for the leaves," said Schadt. "In the leaves, we did see a large effect of fire history on the microbiome that was present, which was somewhat surprising. The leaves obviously weren't directly affected by the fire. They had resprouted and regrown afterward. The leaves had a higher abundance of a couple of potentially pathogenic fungi on the leaves in the burned areas versus the moderate and unburned areas."
Leaves also had less diverse microbiomes overall. Schadt and fellow researchers have several hypotheses for what caused this.
"One might be that aspen is known to have different chemistries of the leaves to deter herbivores like deer from browsing. A lot of times those leaves in full sun areas have a different chemical composition than the leaves in shady areas, and so that could be part of what's changing the microbiome within the high burned areas, or UV light may have an effect because it's much more exposed," he said. "And then the other hypothesis that we have, it's sort of our pet hypothesis right now, is the microbiome that forms on the leaves is known to often come from the surrounding soil. So like it gets blown and deposited onto the leaves. But that soil is the populator of a lot of microbial groups, so it's possible that because that normal microbiome isn't present to colonize from the soil, that that leaves the plant open to colonization from these pathogens."
According to Schadt, this doesn't necessarily mean the saplings will be more vulnerable to disease, but it is likely. He agreed that is included in a lot of options for future research that this study uncovered.
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