LOGAN — A new study published Wednesday in the online journal PLOS ONE has Utah State University researchers both baffled and excited as they try to unravel the wide range of threats to North America's most broadly distributed tree, the aspen.
A startling discovery of a curious genetic pattern was unveiled in the USU-led study, which may also reveal answers behind the slow death that is happening to central Utah's Pando.
Pando, Latin for "I spread," is the world's largest living thing ever discovered on Earth — a 106-acre grove of aspen trees near Fish Lake that is actually one plant consisting of thousands of trees connected by a web of roots. It weighs 13 million pounds.
Called an aspen clone by scientists, Pando has been under siege from dual attacks of drought and bark beetles, and forestry experts fear it could be wiped out within a few years.
What scientists were able to document in aspen is the genetic phenomenon triploidy, which exists in more than half of the clonal colonies of quaking aspen in areas of Utah and Colorado forests.
Triploidy means there are three sets of chromosomes in an organism, instead of the usual set of two — a set from the father and a set from the mother.
Researcher Karen Mock said the majority of the evidence points to Pando being a triploid clone.
"We don't know if triploidy may be a factor in Pando's size and/or a factor in Pando's apparent mortality," said Mock, an associate professor of conservation genetics in USU’s Department of Wildland Resources and Ecology Center. "These triploids do seem to be the larger clones and that suggests they have been especially successful in the past. Something in the past environments in the west has favored them."
Such genetic makeup in plants — a triple set of chromosomes — isn't all that unusual, but the frequency of its occurrence in aspen was documented at a rate off the charts, Mock said.
"In terms of science, it is pretty exciting," she said. "Being triploid is a big difference. It's major. We never dreamed there would be this kind of frequency."
Mock said a common characteristic of triploids is sterility, or at least reduced fertility. Aspen can reproduce from seed or from roots — by throwing out suckers. Triploids, too, have larger cells, which may play into how they disperse water through their system — which could impact how they weather bouts of extreme drought.
Such greater understanding of the aspen is critical on a variety of fronts. The tree, regarded as one of the most important forest species on the North American continent because of its ascetic, ecological and economic value, is dying off in large numbers, particularly in Western landscapes.
Decline is due to drought or disease, but some of it is unexplained, leading scientists to coin aspen mortality as "Sudden Aspen Decline."
The eight-year study — which involved field research in the continental U.S., Canada and Mexico — is exciting because of the breadth of learning opportunities it presents to researchers, Mock said.
"We really don't know how it will play out on the landscape, but it certainly opens up a whole lot of new questions we never knew to ask before."
Along with Mock, the report was written by USU colleagues Paul Wolf, Colin Callahan, Hardeep Rai, Carol Rowe, Ronald Ryel and Richard Gardner, in addition to John D. Shaw and Stewart Sanderson of the U.S. Department of Agriculture Forest Service Rocky Mountain Research Station, Nurul Islam-Faridi of the National Forest Service's Southern Institute of Genetics and Michael Madritch of Appalachian State University.
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