Foliage fossils from forest remains that are estimated to be 23 million years old suggest some plants may have adapted to growing rapidly due to increased CO2 and carbon dioxide, new research suggests.
Scientists found very well-preserved fossil leaves from an ancient lake on New Zealand’s South Island.
This fossil finding enabled scientists for the first time to attribute the high temperatures of that period to high levels of carbon dioxide in the atmosphere.
The results of this latest research have been published in the journal Climate of the Past.
In their scientific paper, the research team shows that some plants are able to harvest carbon dioxide more efficiently for photosynthesis – a biological process that uses sunlight to produce food for these plants.
They say the findings may provide clues to how the dynamics of plant life could shift as carbon dioxide levels have risen to meet its needs in the past.
What can we learn from these ancient leaves?
The research team drilled 100 meters deep to get closer to the now dry lake bottom. It is located in the crater of a long extinct volcano. The area of the crater is about one kilometer.
Here, various biological materials have been fossilized, including the remains of plants, algae, spiders, beetles, flies, fungi, and other living things from a warm period known as the Early Miocene Period.
It is estimated that mean global temperatures were between 3C and 7C higher than today, and most of the ice has disappeared from the poles.
There was debate among scientists about carbon dioxide levels in that period. This is where this research gets really interesting.
“The amazing thing is that these leaves are basically mummies, so we have the original chemical composition, and can see all the subtle features under a microscope,” said lead researcher, Tammo Reichgelt, of the University of Connecticut in Storrs, United States.
Reichgelt said the leaves were so perfectly preserved that the microscopic blood vessels and stomata – the pores that allow the leaves to absorb air and release water during photosynthesis – could be seen.
Scientists analyzed the various chemical forms of carbon – or carbon isotopes – in the leaves of half a dozen tree species found at various levels in sediment.
Jennifer Bannister / Uni OtagoThese findings helped the research team to estimate the carbon content in the atmosphere at that time.
They concluded that the carbon content was about 450 parts se per million (part per milion/ppm).
Previous studies – especially those using marine organisms – have shown that they are significantly lower, at around 300 ppm.
This total carbon content is similar to pre-industrial conditions, and is not sufficient to explain the much higher temperatures of the early Miocene period.
Human activities that release carbon gas today have pushed levels of carbon dioxide (CO2) to around 415 ppm.
This release of carbon gas by humans is expected to reach 450 ppm in the coming decades – the same level experienced by forests in New Zealand 23 million years ago.
William D’AndreaThe researchers also analyzed the stomata geometry of leaves and other anatomical features, and compared them to the presence of leaves in modern times.
They demonstrated that trees are very efficient at sequestering carbon through the stomata, without wasting much water along the same route – a major challenge for all plants.
This allows trees to grow in marginal areas.
The researchers say this higher efficiency is likely reflected in forested areas in temperate northern latitudes, where most of the land area is dominated.
What is that disclosed these findings about the current situation?
When carbon dioxide levels increase, many plants increase their photosynthetic rate, because they can remove carbon from the air more efficiently, and conserve water while doing so.
Data from NASA satellites showing the “global greening” effect mainly due to increased levels of carbon dioxide released by human activities over the last few decades.
It is estimated that a quarter to half of the planet’s vegetated land has experienced an increase in leaf volume on trees and vegetation since around 1980.
Tammo ReichgeltThe effects are expected to continue as carbon dioxide (CO2) levels increase.
But the researchers say that we cannot assume that this is good news.
The increase in CO2 sequestration will not come close to compensating for what human activities release into the air.
And, because much of today’s plant life evolved in a temperate, low-CO2 world, some natural and agricultural ecosystems can be severely disturbed by higher levels of CO2, along with rising temperatures and the resulting shifts in rainfall.
Not all plants benefit, and among those who do, yields may vary depending on temperature and availability of water or nutrients.
There is evidence that when some major plants photosynthesize more rapidly, they absorb less calcium, iron, zinc, and other minerals essential for human nutrition.
“How it turned out seemed to be everyone’s guess,” said Dr Reichgelt. “That’s another layer of stress for plants. Maybe good for some, and terrible for others.”
How can the leaves be properly cared for?
The estate is located on a ranch near the city of Dunedin, in southern New Zealand.
In ancient crater lakes, successive layers of sediment formed from the surrounding environment over tens of millions of years.
The lake is very deep and has low oxygen levels at the bottom. This means that any prehistoric leaf that sank there was relatively well preserved, even though it was 23 million years old.
Jennifer Bannister / Uni OtagoThese include the countless foliage of green sub-tropical forests.
The deposits have a layered structure of blackish organic material interspersed with bands of white silica-rich material formed by algae blooming every spring.
This feature has only been recognized in the last 15 years or so; scientists nicknamed it Foulden Maar.
It is the only known deposit of its kind in the southern hemisphere, and much better than that known from the northern hemisphere.
How does it feel to work with such ancient materials?
Tammo Reichgelt said he felt a great deal of responsibility and “a strange kind of respect” working with such quality fossils that had long remained undisturbed.
He described the process of excavating fossils from holes dug to the bottom of the crater.
The fossils were already exposed to “very windy, sunny and saturated rain” elements.
This fact makes the job very challenging.
“The biggest leaves I have ever found were on a wet day and a handful of brittle stones melted in my hand with leaves on them,” he told the BBC.
“Nothing can save him. When this kind of thing happens, your stomach gets nauseous and you feel like you just destroyed a pharaoh’s tomb.”
Follow Justin ono Twitter.
–
