London: Mushrooms may be the culprit behind the shortage of coal on Earth, as scientists claim to have found evidence that shows the arrival of fleshy fungi species may have stopped the formation of coal deposits about 300 million years ago.
Coal is actually the fossilised remains of plants that lived from around 360 to 300 million years ago. But at the end of that period, coal stooped forming.
Now, scientists found evidence that show the evolution of fungi, which are capable of fully digesting plants, may have stopped dead plants building up into peat and then forming into coal. The discovery might pave the way for new biofuels, the researchers said.
"We're hoping this will get into the biology and geology textbooks," study researcher David Hibbett, a Clark University biologist, was quoted as saying by the Daily Mail.
In the research, Hibbett and his colleagues focused on Basidiomycetes, which include mushroom species with the familiar cap-and-stem look.
Basidiomycetes also include brown rot fungi such as the dry rot that can destroy houses by breaking down the cellulose in the construction wood but leave the lignin untouched; and white rot fungi of interest to the pulp and paper industries that can break down both types of polymers.
The researchers then used molecular clock analyses to track the evolution of the enzymes back through the fungal lineages. The idea is that just as the hands of a clock move at a defined rate around the dial, genes accumulate mutations at a roughly constant rate.
This rate of change allowed the team to work backwards, estimating when two lineages last shared a common ancestor based on the amount of divergence.
It showed that around 290 million years ago, right at the end of the Carboniferous period, a white rot fungal ancestor with the capacity to break down lignin appeared.
Prior to that fungi didn't have that ability and thus the lignin in plant matter was not degraded, which allowed these lignin-rich residues to build up in soil over time, the researchers said.
"When you read about coal formation it's usually explained in terms of physical processes, and that the rate of coal deposition just crashed at the end of the Permo-Carboniferous. Why was that? There are various explanations," said Hibbett.
"The evolution of white rot fungi could've been a factor -- perhaps a major factor. Once you have white rot you can break down lignin, the major precursor of coal.
"So the evolution of white rot is a very important event in the evolution of carbon cycle," Hibbett added.
Kenneth Nealson of the University of Southern California said: "The concept of the invention of an enzyme that can break down the 'unbreakable' is really great."
"The idea that a stable (inedible) form of organic carbon can become edible (and thus more difficult to bury over time), changes our perspective not only on global energy storage in the past, but on what it means for present day carbon sequestration and storage, in that sense this idea will have a big impact on our thinking about the past and the present."
First Published: Wednesday, August 01, 2012, 12:17