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Supporting Links- Plant Adaptions to Life on Land

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Supporting Links- Plant Adaptions to Life on Land

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Supporting Links- The Evolution of Seed Plants and Adoptions for Land

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Supporting Links- The Evolution of Seed Plants and Adoptions for Land

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1.) AM fungi appear to affect D. lanuginosum plants grown at high temperature by increasing their mean root diameter and dry weight of shoots, but decreasing their total root length.
2.) D. lanuginosum plants do not grow equally well when the soil is inoculated with thermal and nonthermal AM fungi.  They grow better when inoculated with nonthermal AM fungi. This suggests that the AM fungi from geothermal and grassland soils have a higher thermal tolerance than D. lanuginosum since they are used to assist D. lanuginosum plants in growing in hot environments.
3.) Average Hyphal length (m/g):
25 degrees Celsius: 1.3
35 degrees Celsius: 0.4
Average Root Length (cm/g):
25 degrees Celsius: 8
35 degrees Celsius: 0
4.) The graph suggests that the D. lanuginosum roots and fungal hyphae have a rather low relative heat tolerance, because they grow best at about 20 degrees celsius and decrease in size if the temperature goes up. This explains the differences in growth of D. lanuginosum plants grown in soils with and without AM fungi, because the AM fungi helps plants grow in high-temperature soils. The plants without the AM fungi did not grow as much as the plants with the AM fungi, because they were not getting assistance since they struggle to grow as much in high temperatures.

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Start studying AP Biology Chapter 26 Vocabulary. Learn vocabulary, terms, and more with flashcards, games, and other study tools.

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- 26.1
Fossils show that plants colonized land more that 470 million years ago.
- 26.2
Fungi played an essential role in the colonization of land.
- All fungi are heterotrophic.
- 26.3
Early land plants radiated into a diverse set of lineages.
- The closest relative to plants is the charophyte algae, which is similar except for its absence of an alteration of generations, like the plants do.
- In the cycle of plant life with alteration of generations, there are sporophytes which are the asexual and diploid phase.
- Animals are considered to be the closest relative to fungi.
- 26.4
Seeds and pollen grains are key adaptions for life on land.
- Conditions such as having a large surface area and access to many nutrients are a key factor in fungal mycelia having adaptive advantages related to their filamentous nature.
- 26.5
Land Plants and Fungi fundamentally changed chemical cycling and biotic interactions.

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Supporting Links- Fungi and its Influence on Land Evolution

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Supporting Links- Fungi and its Influence on Land Evolution

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Lichens and moss covering rocks in Pennsylvania. Did Precambrian land look like this? Photo Credit: David Geiser, Penn State

The largest genetic study ever performed to learn when land plants and fungi first appeared on the Earth has revealed a plausible biological cause for two major climate events: the Snowball Earth eras, when ice periodically covered the globe, and the era called the Cambrian Explosion, which produced the first fossils of almost all major categories of animals living today.

According to the authors of the study, which will be published in the 10 August 2001 issue of the journal Science, plants paved the way for the evolution of land animals by simultaneously increasing the percentage of oxygen in the Earth's atmosphere and decreasing the percentage of carbon dioxide, a powerful greenhouse gas.

"Our research shows that land plants and fungi evolved much earlier than previously thought - before the Snowball Earth and Cambrian Explosion events - suggesting their presence could have had a profound effect on the climate and the evolution of life on Earth," says Blair Hedges, an evolutionary biologist and leader of the Penn State research team that performed the study.

The researchers found that land plants had evolved on Earth by about 700 million years ago and land fungi by about 1,300 million years ago - much earlier than previous estimates of around 480 million years ago, which were based on the earliest fossils of those organisms. Prior to this study, it was believed that Earth's landscape at that time was covered with barren rocks harboring nothing more than some bacteria and possibly some algae. No undisputed fossils of the earliest land plants and fungi have been found in rocks formed during the Precambrian period, says Hedges, possibly because their primitive bodies were too soft to turn into fossils.

The early appearance on the land of fungi and plants suggests their plausible role in both the mysterious lowering of the Earth's surface temperature during the series of Snowball Earth events roughly 750 million to 580 million years ago and the sudden appearance of many new species of fossil animals during the Cambrian Explosion era roughly 530 million years ago. "Both the lowering of the Earth's surface temperature and the evolution of many new types of animals could result from a decrease in atmospheric carbon dioxide and a rise in oxygen caused by the presence on land of lichen fungi and plants at this time, which our research suggests," Hedges says.

"An increase in land plant abundance may have occurred at the time just before the period known as the Cambrian Explosion, when the next Snowball Earth period failed to occur because temperatures did not get quite cold enough," Hedges says. "The plants conceivably boosted oxygen levels in the atmosphere high enough for animals to develop skeletons, grow larger, and diversify."

Lichens are believed to have been the first fungi to team up with photosynthesizing organisms like cyanobacteria and green algae. Lichens can live without rain for months, providing protection for photosynthesizing organisms, which produce oxygen and release it into the atmosphere. The researchers suggest that the pioneer lichen fungi, which produce acids strong enough to dissolve rocks, also could have helped to reduce carbon dioxide. When washed away by rainwater, the calcium released from the lichen-encrusted rocks eventually forms calcium carbonate limestone in the ocean, preventing the carbon atoms from forming the greenhouse gas, carbon dioxide, in the atmosphere.

Land plants also can lower levels of carbon dioxide in the atmosphere. They have molecules called lignins, which contain carbon but do not readily decompose. After the plant dies, some of its carbon remains locked up in the lignins and can become buried in the Earth through geologic processes, preventing those carbon atoms from returning to the atmosphere and effectively lowering atmospheric carbon dioxide.

Lichens and moss covering rocks in Pennsylvania. Photo Credit: David Geiser, Penn State

"The Earth cools when you take away carbon dioxide," Hedges says. "Other factors such as the location of the continents may have had some effect in cooling the atmosphere and creating periods of Snowball Earth, but I suspect the biggest cooling effect came from the reduction of carbon dioxide in the atmosphere by fungi and plants, which we have shown were living on the land at that time."

Fossil fuels like coal and oil are made from plant material, containing carbon that was taken out of the atmosphere and buried in swamps millions of years ago. Releasing those same carbon atoms back into the atmosphere by burning fossil fuels appears to be causing the Earth to get warmer again, according to many studies.

Hedges and his research team made their surprising discoveries about the early appearance on Earth of the first land plants and fungi by studying as many of the genes as possible of their descendants - the species of plants and fungi living today. They began by sifting through their molecular fingerprints - the unique sequences of amino-acid building blocks - in many thousands of genes from hundreds of species archived in the public gene-sequence databases.

Eventually, they found 119 genes common to living species of fungi, plants, and animals that met the researchers' stringent criteria for use as "molecular clocks." Previous studies had used a single gene. By detailed comparisons of the amino-acid sequences of individual genes among numbers of species, the scientists identified those genes that had accumulated mutations at a fairly constant rate relative to one another during their evolution. "Because mutations start occurring at regular intervals in these genes as soon as a new species evolves - like the ticking of a clock - we can use them to trace the evolutionary history of a species back to its time of origin," Hedges explains.

The scientists calibrated each of their gene clocks with evolutionary events well established by fossil studies, primarily those in the history of animals. Using these known dates as secure calibration points, and the mutation rate for each of the constant-rate genes as a timing device, the researchers were able to determine how long ago each of the species originated.

Hedges says his research might help in the search for life on other planets by providing a link between the different stages of life's evolution on Earth and the timing of events in the chemical evolution of Earth's atmosphere, such as the rise in oxygen. "Possibly the early history of life on Earth can give us clues for predicting the kinds of lifeforms that are likely to exist on planets in other solar systems from the chemical content of their atmospheres," Hedges says.

In addition to Hedges, the Penn State research team includes Daniel S. Heckman, an undergraduate student whose senior honors thesis formed part of this research; David M. Geiser, assistant professor of plant pathology; and undergraduate students Brooke R. Eidell; Rebecca L. Stauffer; and Natalie L. Kardos. This research was supported, in part, by the National Aeronautics and Space Administration through the Penn State Astrobiology Research Center.

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CONTACT:
Blair Hedges, 814-865-9991, sbh1@psu.edu
Barbara K. Kennedy, 814-863-4682, science@psu.edu
IMAGES:
Additional high-quality color images of lichen are available directly from Stephen Sharnoff, a professional photographer and colleague of the researchers, via e-mail at lichen@idiom.com, telephone at 510-548-9189, or postal service at 2406 Roosevelt Ave., Berkeley, CA 94703.

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First Land Plants and Fungi Changed Earth's Climate, Paving the Way for Explosive Evolution of Land Animals, New Gene Study Suggests

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Lichens and moss covering rocks in Pennsylvania. Did Precambrian land look like this? Photo Credit: David Geiser, Penn State The largest genetic study ever performed to learn when land plants and fungi first appeared on the Earth has revealed a plausible biological cause for two major climate events: the Snowball Earth eras, when ice periodically covered the globe, and the era called the Cambrian Explosion, which produced the first fossils of almost all major categories of animals living today.