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Fossilized Pollen may reveal ‘fingerprints of environmental stress’

Fossilized Pollen may reveal ‘fingerprints of environmental stress’

Fossilized pollen may reveal fingerprints of environmental stress
Fossilized pollen may reveal fingerprints of environmental stress
Credit: Burke Museum

Around this time each year, we start to recognize the existence and microscopic reproductive cells of cone bearing and flowering plants. While pollen from the air may cause congestion for some, a new paper reveals that these grains may offer a new way to view the climate 300 million years ago in the fossil record.


Jeffrey Benca, Burke Museum Research Associates, thinks year-round about pollen. His newpaper in The Journal PaleobiologyThis study examines what pollen malformations (or abnormally shaped pollen grains) can tell us about stress in our environment. Previous studies have shown that environmental pollutants and increased UV-B radiation exposure can alter the shape of pollen grains cone-bearing tree trees produce, and even make them temporarily sterile.

Benca and his colleagues studied how often these malformations could be produced in a variety of living conifer types. They also examined what abnormal pollen shapes they produced when exposed to different levels of environmental stress.

The fossil record of pollen has hundreds of millions of years of history. It is well documented. Many types have a hard coating which makes them more likely be preserved in fossil records. Conifer pollen is also considered to be airborne. It rides the wind and falls across vast swathes, both land- and water-based. These pollen grains are particularly useful in looking at long-term climate change because they accumulate in environments that are conducive to fossilization. They can also be found in many different ages.

Benca stated that pollen can be rained into the ocean, where we can see the marine animal records. This allows us to get a snapshot of the ocean’s animals and plants at the same moment, which is very unusual. The pollen records have given us an insight into how you can take a walnut-sized amount of sediment and reconstruct kilometers upon kilometers of forests and ecosystems. It’s a powerful technique to try to get a larger picture of what’s happening.

He and his coauthors Cindy Looy, Ivo Duijnstee & Cindy Looy, sampled pollen grains of 14 different species of conifers while at University of California Berkeley. These conifers were mostly grown in their Botanical Garden. These trees can be considered as low-stress because they are provided with adequate water and care by their landscaping staff. Under baseline conditions, all 14 species showed a malformation rate below 3%. Studies from the past suggest this.Based on historical field observations, it is normal for conifers in low stress.

They exposed one modern pine species, which is essentially simulating an event that weakens the ozone layer, to high levels UV-B radiation. This caused them to produce a higher rate of malformed flowers. They also produced more uniform malformations in trees that were exposed to high UV-B radiation doses.

Benca stated that it was a sign that the tree was extremely stressed. “It’s leaving an impression or a mark that it’s not doing well.

These conifer plants often produce pollen called bisaccate grain, or winged-pollen grains. Imagine a Mickey Mouse head with one large pollen grain at the center and two smaller wings that branch off to the sides. These wings, also called sacci or sacci help the pollen grains ride on the wind, sometimes hundreds miles away from where they were grown.

These trees produced a mixture of different malformations when they were under low stress conditions. Some had one wing, others three. However, trees were more likely to produce three-winged malformations from UV-B radiation.

The researchers suggest that you can use the 3% rule to identify times when environmental stress is high. However, you may also be able use certain types malformations to determine the type of stress long-extinct plants were under. In this instance, a spike of three-winged pollen grains might indicate ozone weakening events.

Benca said, “The crazy thing is that the trees were flourishing.” “They looked like they had been grown in a garden and not under these horrible UV radiations. We thought back to the possibility that if you were walking around a mass extinction with an Ozone weakening event, it would not be obvious until you get sunburnt. The trees would still look great.

Numerous ozone-depleting events may have occurred throughout the history of earth’s existence, largely due volcanic activity like the Siberian Traps formation 250 million years ago. This volcanic event was the most significant in the last half-billion years and is believed have caused the largest mass extermination event on earth, the End-Permian Extinction.

Recent events have seen an ozone depletion over Antarctica as a result of man-made aerosols produced by products such as refrigerators, hairspray, air conditioners, and air conditioners. The Montreal Protocol had a severe limit on the use of certain chemicals. But the ozone layer began healing.

To measure the current ozone layer, we don’t need to use pollen as a proxy; we can do it directly. It can be a powerful tool to examine the past for insights into how ecosystems have reacted to increased environmental stressors like climate change and mass extinctions. Other environmental stressors, such as heavy metals, acid rain or pathogens, may also produce unique pollen malformations which we can use for better understanding the past.

Benca hopes to explore some of these questions with modern plants and pollen from the fossil record in the future. It was rare to see how different lineages of conifers from different hemispheres responded to the same environmental conditions by comparing 14 different species of tropical and temperate conifers grown in the same gardens.

Researchers can more confidently use pollen abnormalities as a stress indicator in fossil records because of the low rate at which malformations occur in garden trees. Researchers hope to be able to identify regional patterns in pollen malformations in the fossil record. This will allow for stress detection in the fossil records. Future studies will examine how trees at different elevations and locations might produce different malformations.

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More information:
Jeffrey P. Benca and Ivo A. P. duijnstee, Cindy V. Looy. Fossilized Pollen Malformations as Indicators of Past Environmental Stress and Meiotic Disruption: Lessons from Modern Conifers Paleobiology (2022). DOI: 10.1017/pab.2022.3. doi.org/10.1017/pab.2022.3

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Burke Museum

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Fossilized pollen could reveal environmental stress ‘fingerprints,’ (2022, April 22).
Retrieved 22 April 2022
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