Month: April 2019

To begin our journey, I climbed Stone Mountain to discover the symbiotic relation of fungi and algae, or cyanobacteria, called lichen. Transitioning from the discussion of their cell structures and the life cycles, we shift our attention to the last stage of our journey now to the usage of lichens to detect air pollution within the environment. 

The study of air pollution and the impact of lichen can be observed as early as 1791 in a poem written by Erasmus Darwin, where he states, “No grassy mantle hides the sable hills, / No flowery chaplet crowns the trickling rills, / Nor tufted moss nor leathery lichen creeps / In russet tapestry o’er the crumbling steeps” (Darwin, 1791). This line implicates the effect of copper mines within the area and the effect of the pollution on the surrounding ecosystem, signaled by the nature of the lichen. Since they are strong enough to grow on bare rock but remain easily susceptible to air quality, air pollution directly affects their growth, reproductive potential, morphology, and physiological processes. Tracking these features can reflect significant changes in their respective environments (Nash III, Gries, 1991).

While many plants are used to detect environment changes, lichens are most closely studied in relation to sulphur dioxide present in air pollution (Nash III, Gries, 1991). Sulphur dioxide is absorbed by the fungal part of the lichen, destroying the chlorophyll portion of the algal partner, which inhibits photosynthesis. In order for the algal partner to survive in high pollution areas, the algae supercedes its symbiotic relationship with the fungi and begins to develop independently (Pescott, 2015). Thus the presence of green algae can indicate high levels of pollution.

Sulphur dioxide has caused some species of lichen to become extinct in areas with high levels of air pollution. Certain species of lichen have a higher tolerance for air pollution than others, and the study of which species can be located in certain areas can show how poor the air quality is. Lepraria incana is a species that can tolerate poor air quality of 125 µg/m3 of sulphur dioxide; meanwhile, more sensitive species like Lobaria amplissima cannot tolerate any sulphur dioxide (UK, n.d.). An abundance of Lepraria incana can indicate less competition in an environment, leading to the accumulation of this species. The species of lichen I observed on Stone Mountain is believed to be Lepraria incana, and I observed this species to be present on a multitude of surfaces with little to no diversity. The rise Lepraria incana within Stone Mountain is in line with the rise of soot pollution levels, a byproduct of burning fossil fuels, within the past several  years (Rhone, 2019).

In the future we should become aware of lichen within our environments. Since lichens are helpful tools to help determine air quality levels within cities, understanding lichens relationship will also help us understand the ecosystem the lichen live in. The rise of certain species indicate a rise of air pollution, and if air pollution levels are not controlled, the lichen species will begin to disappear from the environment. This can lead to death of plants and animals within the ecosystem untimely affecting our own well being.

Spongebob with suds is the best way to imagine lichen with the increasing air pollution.

Lobaria amplissima

Lepraria incana

Here’s a video from the natural history museum conducting an air quality experiment using lichen

https://www.youtube.com/watch?v=shl5c73ump0

References

1. Darwin E 1791. The Botanic garden: a poem, in two parts . London: J. Johnson.
2. Nash T.H., Gries C. (1991) Lichens as Indicators of Air Pollution. In: Air Pollution. The Handbook of Environmental Chemistry, vol 4 / 4C. Springer, Berlin, Heidelberg
3. Pescott, O. L., Simkin, J. M., August, T. A., Randle, Z., Dore, A. J., & Botham, M. S. (2015). Air pollution and its effects on lichens, bryophytes, and lichen-feeding Lepidoptera: Review and evidence from biological records. Biological Journal of the Linnean Society, 115(3), 611-635. doi:10.1111/bij.12541
4. Rhone, N. (2019, April 24). DEEPER FINDINGS: Five metro Atlanta counties earn a failing grade for air quality. Retrieved from https://www.ajc.com/news/five-metro-atlanta-counties-earn-failing-grade-for-air-quality/C6Csmoq45khlpJMACq0cKM/
5. U. (n.d.). Air Quality and Lichens. Retrieved April 24, 2019, from http://www.air-quality.org.uk/19.php

About 13,500 species of lichen are composed of fungi that come from the phylum Ascomycota. Ascomycota, depending on which stage of the life cycle they are in, can transform from an asexual phase into a sexual life cycle and vice versa. Ascomycota contains a single-celled spore form––the specific type depends on the species of Ascomycota––and a filamentous mycelium (Taylor, Spatafora, Berbee, 2006).

In the asexual life cycle, the mycelia use specialized hyphae, called conidiophores, to branch off the mycelia and begin producing spores. These spores are called conidia or mitospores and are haploid cells that will undergo mitosis. The spores that complete mitosis will remain dormant and wait until ideal environmental conditions are present in order to germinate to produce new mycelium. Asexual reproduction is the most common form of reproduction as it only involves a single mycelium.

During the sexual reproduction phase, it begins in the mycelium, but unlike asexual reproduction, there will be at least one female and one male mycelium. The males have an antheridium and the females have an ascogonium––their respective reproductive organs. Once the two organs fuse, plasmogamy begins, which is the fusion of the cytoplasm between the two organs. These fused organs are called an ascocarp, and they begin to grow sac-like cells within the ascocarp called ascus. Within the ascus, male and female genetic information is fused in the nuclei when the ascospores undergo karyogamy to form a diploid zygote. The diploid zygote will undergo meiosis, and the ascus will now contain four unique haploid nuclei. The newly formed haploid cells will now undergo mitosis and cell division to form eight haploid spores that are then released and set to germinate and form new hyphae in new environments (Learning, n.d.). Spores can be released by wind, water, mechanical force, or insects. Their goal is to ensure there is less competition for resources and a suitable substrate for germination.

Ascomycota is such a vast phylum that it also contains many different kinds of single-celled yeast. These yeasts mainly reproduce via budding or fission a form of asexual reproduction. Budding is the process where a small portion of the cytoplasm of the parent cell becomes separated and form a daughter cell. Fission is the equal division of the cytoplasm into two daughter cells the same size. Under extreme conditions like starvation, yeasts may reproduce sexually. This happens when two different mating types fuse cytoplasm and nuclei. The process forms a diploid cell where it will undergo the same process as other Ascomycota to release spores.

In order to supply nutrients, Ascomycota is heterotrophs and digest living or dead biomass. They secrete digestive enzymes that break down organic material into small molecules, and the small molecules are absorbed through the cell wall. Depending on the specific species, these fungi can obtain nutrients in almost any imaginable pathway. Most species live on dead plant cells that find their way to the forest floor. Some act as parasites and receive metabolic energy and nutrients from the host’s cells. Ascomycota can also form symbiotic relationships with cyanobacteria, called lichens, where they gain nutrients through photosynthesis. Ascomycota can digest organic substances ranging from plant cellulose all the way to wall paint and aircraft fuel (Foundation, n.d.)

Here’s a quick video showing various species of lichen growing when exposed to nutrients

Sources:

1. Learning, L. (n.d.). Biology for Majors II. Retrieved April 19, 2019, from https://courses.lumenlearning.com/wm-biology2/chapter/ascomycota/
2. Foundation, C. (n.d.). 12 Foundation. Retrieved from https://www.ck12.org/book/CK-12-Biology-Advanced-Concepts/section/12.27/
3. Taylor, J. W., Spatafora, J., & Berbee, M. (2006, October 9). Ascomycota. Retrieved April 19, 2019, from http://tolweb.org/Ascomycota

Just like Patrick discovering the presence of foreign organisms living in his rock, we must find out what these lichen are.

Lichen are not just a singular organism, but are formed from a symbiotic relationship between a fungus and algae or cyanobacteria. A lichen’s thallus structure consists of different layers of algae and fungus called the cortex, photobiont, and medulla. The cortex is the outermost layer and acts like a protective skin. This layer consists of fungal hyphae that are closely packed together. Below the cortex is the photobiont layer, this is where the algae or cyanobacteria reside. Typically if the photobionat layer is algae a brighter green color will resonate from the lichen while a dark blueish-green color will come from a cyanobacteria. Finally, we get to the medulla, which is actually a majority of the lichen’s thallus. It consists of fungal filaments that are loosely packed into the middle and resemble loose threads. 

Now that we have established these organisms are not aliens from another plant, we must find how they are able to stick to everything and anything in order to evict them from Patrick’s home. 

Lichen attach using the one of two mechanisms: Rhizines or Holdfast. Rhinizines use multiple fungal filaments to attach to their surface while holdfast use a central peg to attach to theirs. 

Here’s a video explaining the structure of the lichen

Now its time for Patrick to remove this organisms from his home

We’re SAVED!!!

We’re SAVED!!!

We’re SAVED!!!

It’s a big, beautiful, old rock! Oh, the pioneers used to ride these babies for miles! And it’s in great shape.

For my blog project, I put my life at risk trying to scale the treacherous mountain made of stone. Many dangers include high altitudes and steep slopes you can fall off.

One of the main reasons I choose Stone Mountain is to force myself to do cardio in the name of SCIENCE! Stone Mountain has a one-mile hike up the mountain where the scenery spans across most of metro Atlanta. Stone Mountain is a state park so the natural ecosystem of the park is allowed to thrive within the park. Many wild animals roam the park as well as a thriving community of trees. On these trees, I noticed there were light yellow crusty patches all over the bark.

I discovered this discoloration was due to lichens. The lichen looked as if it was a parasite invading organisms. Upon further research it was discovered, lichen form via a mutualistic relationship between fungi and algae or cyanobacteria. I was excited by this organism because it was literally everywhere. It not only grew on trees but it grew on the rock itself. I believe the lichen I discover is called Lepraria incana. Lepraria incana is one of many indigenous species of lichen within the park.

Here’s a cool short film explaining how we got lichens so wrong.

Special thanks to my girlfriend Jessika for making this dangerous journey with me. Here is her reaction to me telling her I’ve taken a lichen to her whilst on the hike.