Age might well be just a number, but for a plant in Utah known affectionately as Pando, it could be a digit that leaves all other living things in the dust.
Sequencing hundreds of samples of material collected from the vast network of quaking aspen (Populus tremuloides), a team of scientists in the US has estimated the 106-acre (43-hectare) wood may have started as a lonely seedling long before the end of the last ice age, some 34,000 years ago.
Incredibly, less conservative estimates confirm it’s possible that the tree may have even sprouted tens of thousands of years before that.
Though the study is yet to be peer reviewed, its conclusions help confine speculations over how long this one clonal organism has stood in place, which have ranged wildly from several thousand to more than a million years.
Pando already attracts attention from biologists for its impressive size, considered by some to be the single largest organism on the planet.
Though the aspen appears to be 47,000 distinct trees rising above the soil, all share the same genetic heritage and the one web of interconnected roots, effectively making them all chips off the same ol’ block.
The record holder for a solitary tree’s age is an unnamed bristlecone pine in California’s White Mountains, thought to be a smidge over 5,000 years old.
Yet clonal organisms like Pando – a name that translates into ‘I spread’ – play by different rules. Its genome of chromosome triplets doesn’t mix easily with others within its species, limiting the plant’s reproduction to asexual clones that remain connected while rooting its way through the environment.
Whether we consider creeping populations of near-identical cells to be one individual or an army of closely-related units, clonal organisms have a knack for persisting in one place where their sexually-reproductive cousins easily whither. Asexual reproduction has allowed some species of fungi to survive for centuries in one place as a single ongoing mass, for example.
Pando has already been suspected of being extremely old. To place harder limits on its actual age, the research team collected around 500 pieces of root, leaf, and bark from its trees, as well as specimens from other, unrelated aspen, and sequenced their DNA.
Applying analytical techniques to pick out changes that have emerged over time, the researchers identified 4,000 genetic variations across the various samples. The patterns of their mutations told an intriguing story, one their models suggest dates back anywhere from 16,000 to 80,000 years.
“You would expect that the trees that are spatially close are also closer genetically,” University of Chicago geneticist Rozenn Pineau told Helena Kudiabor at Nature.
“But this is not exactly what we find. We found a spatial signal, but that is much weaker than what we expected.”
Further studies on why its history of mutations has spread in this way and how Pando protects its genome to avoid accumulations of less-helpful genes could tell us why the plant and others like it live to such a ripe old age.
With fears that Pando’s days might be numbered, it’s critical we learn as much as we can about the plant’s ability to handle whatever humans and the natural world might throw at it.
Similar studies on other clonal organisms may even push the aspen from its perch. There’s a patch of Posidonia oceanica seagrass off the Spanish island of Formentera which some venture might be more than 200,000 years old.
We can only hope Pando sticks around to reach such a number.
This research is available on the pre-publish server bioRxiv.
