The Use of Lichens as Bioindicators

By Amy Baumann
Cheltenham High School, Pennsylvania
Grade 9

Abstract

The purpose for this experiment is to investigate the effect of acidic solution on fruticose, foliose, and crustose lichens. This experiment is being done to model the effect of acid rain on lichens in the natural environment and to use this information to determine if these lichens can be used as bioindicators.

The hypothesis for this experiment is that the fruticose lichen samples will be the most susceptible to the acidic solution over the ten day period. This is because the fruticose lichen is a sign that the air is clean. The foliose lichen samples will be the next most susceptible to the acidic solution. The crustose lichen samples will be the least susceptible to the acidic solution because this type of lichen is a sign the air is dirty and polluted.

At the end of ten days there was a considerable difference in the lichens misted daily with water, or the control, and the lichen samples misted with acidic solution. The fruticose and foliose lichens in the control grew very well in both tests. Also, each turned a deep color and was healthy at the end of the ten days. The control sample of the crustose lichen seemed to be unresponsive to the water in both tests. The samples seemed to not change in growth or color. In the samples misted with acidic solution, the fruticose and foliose lichens grew poorly in comparison to the control samples. Also, the fruticose sample turned a yellowish-brown in contrast to the deep green of the control samples. The acidic foliose samples turned orange only around the edges compared to the control samples which were completely orange. The crustose sample grew better in the acidic environment, as it grew new thalluses and turned a green color.

The results of the experiment partially support the hypothesis. The crustose samples were the least susceptible to the acidic solution, but the foliose samples were the most susceptible. Also, these lichens can be used as bioindicators. Through the results it is known that if an area is populated with crustose lichens, the area is unhealthy and polluted.

Test 1 Control (on left) and Acidic (on right)

Test 2 Control (on left) and Acidic (on right)

Results

In all three lichen samples in both experiments, there was a considerable difference between the control lichens and the lichens fed with acidic solution after ten days of experimenting. Figure 1 shows the fruticose, foliose, and crustose lichens on the first day of experimenting. In these control samples, the lichens flourished and grew rapidly. As shown in Table I, the fruticose samples of the first test had thalluses that stretched out vertically in both directions. In the foliose samples, new thalluses formed and grew tall on the substrate. Also shown in Table I, the crustose sample did not experience the growth that both the fruticose and foliose control samples did. Barely any new thalluses formed during the ten days.

In the control samples, the colors of the lichens changed as the days went by. Shown in Table II, the fruticose samples varied in different greens, turning deep green by the seventh day in test one. The foliose samples turned an orange shade almost immediately. In four days, the lichens had turned completely dark orange. The crustose lichens responded the least to just water. The color of the few thalluses that formed were a greenish-brown. Figure 2 shows the control samples for the first experiment on the tenth day.

Although the fruticose and foliose control samples flourished under a normal water environment, the fruticose and foliose samples under acidic solution did not mature nearly as well. Figure 3 shows the acidic lichen samples on the first day of experimenting. As shown in Table I, the fruticose lichens exhibited little growth in all ten days of the first experiment. Hardly any new thalluses were formed and the present thalluses grew very little in comparison to those of the control fruticose samples. Also shown in Table I is the minimal growth of the foliose lichen samples fed with acidic solution. In contrast to the upward growth of the control foliose samples, the acidic samples grew flat and short. The crustose lichens exposed to the acidic solution in test one grew well in comparison to the control crustose samples. New thalluses formed and grew upright to the substrate, as shown in Table I.

As in the control samples of the first test, the color of the acidic lichens changed during the ten days of experimenting. In contrast to the control sample, the acidic samples changed to brittle, drab colors, with the exception of the crustose sample. Shown in Table II, the fruticose samples turned a yellowish light green and the foliose samples only turned orange at the tips of the thalluses. The crustose samples stayed the green they were at the beginning of the ten day experiment. Figure 4 captures the acidic lichens from the first test on the tenth day.

The results of the second experiment supported the accuracy of the first. Figure 5 shows the control lichen samples for the second experiment on the first day. As shown in Table III, the fruticose and foliose control samples grew very well and the crustose sample stayed almost the same. The fruticose and foliose lichens exposed to acidic solution showed minimal growth in comparison, and the crustose sample grew new thalluses and flourished in the acidic environment. Figure 6 shows the acidic lichen samples on the first day of the second test.

Table IV shows the colors of the control and acidic samples in the second test. As in the first test, the fruticose and foliose control samples turned into deep and vibrant colors. The crustose sample stayed a brownish-green throughout. Figure 7 shows the control lichen samples at the end of the tenth day of experimenting. The fruticose and foliose acidic samples turned drab and dull colors while the crustose sample turned a bright green. Figure 8 shows the acidic lichen samples on the tenth day of the second experiment.

It is important to mention that this experiment is an observational study of the effect of acidic solution on lichens. The data collected in the report is strictly observation. Finding the masses of the lichens to show growth before and after the ten days was considered, but the slight weight change would not effectively illustrate the great differences between the control lichens and the lichens under the acidic solution. The difference in the types of lichen structures also made it impossible to measure a simple length or width of a single thallus. Therefore, the hypothesis is supported through photographs and detailed observation.

Introduction

This experiment is investigating the effect of acidic solution on different samples of lichens to model the effects of acid rain on lichens in the natural environment. For the experiment, samples of crustose, foliose, and fruticose lichens are being used. This information is also being used to conclude if these lichens can be used as bioindicators.

Lichens are two-part organisms made from a combination of both alga and fungus(Bland 1971). Though the alga and the fungus are partners, the alga can live separately, where as the fungus cannot(Hutchins 1966). The alga and fungus work together in the thallus, the body and growing part of a lichen. There, the alga is necessary for the survival of fungus. Alga, through photosynthesis, makes sugar from carbon-dioxide and water. Fungus is known to be parasitic on the alga. In primitive lichens, the fungus gains its nutrients through the haustoria, an organ which absorbs food by piercing the alga cells. In higher forms of lichens, the fungus clasps to the algal cell surface(Bland 1971). The relationship between the algae and fungi in lichens is not just one-sided. Though the alga provides the fungus with food and moisture, the fungus provides the alga with protection as the outside surface of lichens are made up of fungus tissue(Hutchins 1966). Also, alga can not effectively collect water. This job is carried out by the fungus(Bland 1966).

Lichens can reproduce in many different ways. In sexual reproduction, the lichens produce sacs that contain spores produced by sex cells. When these fungal spores are mature, they are let go into the air during wet weather. The spores then find a satisfying spot where they become tiny seeds and absorb moisture and food from the surface around them. Soon the fungus comes into contact with algal cells in the same area. The fungus takes them over and begins to depend on the algal cells for its food. In another method of reproduction, tiny clumps of fungus, known as soredia, are produced by the lichens. The soredia forms on the surface of the lichens and when blown away they settle and mature. Still another way lichens can reproduce is called fragmentation. This occurs when very dry and brittle parts of lichens break off. If these parts settle in a moist area, they will attach themselves and grow(Hutchins 1966).

Lichens are classified in three types. Crustose, foliose, and fruticose. Crustose lichens are the most primitive and non-showy of all three types(Bland 1971). They grow on rocks and tree bark and attach themselves so tightly against a surface, they are difficult to pull off(Hutchins 1966). An example of crustose lichens are Sod Lichens which are found on the ground in the Eastern United States(Bland 1971). Foliose lichens are dainty and leaf- like, growing on rocks and trees. They have two growth forms. Foliose lichens can grow by attaching themselves to a substrate, the object they grow off of, by the underside of the thallus, or they can erect from a circular thallus growing from the center point of a substrate(Bland 1971). Dog Lichen is an example of a foliose lichen(Hutchins 1966). Fruticose are the most specialized and highest form of lichen(Bland 1971). They grow vertically to the ground or hang from limbs of trees. These lichens are branching and are usually described as being shrubby. A good example of fruticose lichen is Old-Man's-Beard, which hangs from trees(Hutchins 1971). Lichens have sizes that can vary from a few millimeters to thousands of millimeters(Bland 1971). They also have varying colors that can range from golds and pinks to blues and greens(Hutchins 1966).

A main part of this experiment deals with acid rain. Today, exhaust from engines and high stack emissions have led to acid rain becoming a pollutant of importance(ed. Hawksworth 1991). Acid rain is caused when gases, such as sulphur dioxide and nitrous oxide are released into the air. These gases mix with water vapor to form sulfuric and nitric acid. When acid rain falls it is dangerous to many parts of the environment. When it gets into rivers it can kill aquatic life and increase the acidity of soil and ground water. Acid rain is also known to erode buildings and monuments(Paxton, 1996).

Acid rain and pollution are a main factor in the killing of lichens all around the world. Because of their sensitivity to pollution, lichens are very good bioindicators. Bioindicators are living organisms that respond in an especially clear way to a change in the environment(Lichens as Bioindicators 1996). Lichens can be used to tell so much about pollution levels because they absorb water and gas from the air. Also, many types can't survive in polluted environments(Katz 1986). Lichens lack a protective surface that can block out these pollutants. They don't have roots, stems, or leaves so they have to get their nutrients from rainwater(Lyman 1996). Lichens absorb gases and vapor through tiny round shaped holes called cyphellae(Bland 1971). When they absorb acid rain, the sulfur dioxide and the nitric oxide destroy the chlorophyll molecules that are responsible for photosynthesis. When this occurs the algae dies, and due to its reliance on the algae, the fungus dies killing the lichen(Lyman 1996).

Many past experiments and tests have been done to show pollution's effect on lichens. In the British Isles, the lichen species of Usnea was widespread until eighteen hundred. As a result of increasing pollution, the species disappeared from an area of seventy thousand kilometers squared (ed. Hawksworth 1991). In Norway, a company named Pechenganikel was made in 1933. In nineteen forty-four it was taken over by the Soviet Union. Before nineteen seventy-three, the emission of sulphur dioxide never exceeded one hundred thousand tons per year. At that point a chemical named nickel was being used that only had a six and one- half percent sulfur content. After nineteen seventy-four, the industry used new nickel that had a sulphur content of thirty percent. The emissions of sulphur dioxide as a result of the new nickel being used increased up to four-hundred-thousand tons in nineteen seventy-nine. Through research, it was found that the nickel concentrations in lichens showed an increase of thirty times in the most affected area. The study also showed the deterioration of the lichen environment through their decrease in existence, covering seven-hundred-fifty kilometers squared on the Russian and Norwegian border caused by air pollution(Torrmervik 1996).

The hypothesis for this experiment is that the fruticose lichen samples will be the most susceptible and die due to the acidic solution. This "shrubby" lichen is a sign that the air is clean(Wilkes 1991). The foliose lichen samples will be the next most susceptible to the acidic solution. The crustose lichen samples will be the least susceptible to the acidic solution. These crusty lichens are know to be able to survive in polluted areas and show that the air is dirty(Walpole 1988).

Methods and Materials

To study the effect of acid rain on different samples of lichens, I first ordered two lichen sets that included portions of crustose, foliose, and fruticose lichens from the Carolina Biological Supply Company. I then took both sets of lichens and placed each individual sample into its own glass jar. I then filled one spray bottle with 10 ounces of Dannon bottled water. I placed a label on the spay bottle and labeled it water. I took a slit of white tape a put it on one of the ditches in the twisting top to the spray bottle. I then turned it around four times. I then filled half of the other spray bottle with 5 ounces of vinegar and the other half with 5 ounces of Dannon bottled water. I did this because acid rain has the same effect on plants and organisms as water and vinegar mixed together; only vinegar and water works slower and is weaker(Wilkes 1991). I then placed a label on the spray bottle and labeled it acid. I took a slit of white tape and put it a ditch of the twisting top of this spray bottle. I then turned it four times so the mist settings of both bottles were the same. I then took a sample of crustose, foliose, and fruticose lichens and used them as a control, misting them daily with water. After I misted each sample three times with water I placed Saran wrap on the opening in the jars and sealed it with a rubber band. I then took the remaining samples of crustose, foliose, and fruticose lichens and misted them daily with the acid. After I misted each sample with the acid three times I placed Saran wrap over the opening in the jars and secured it with a rubberband. Everyday I took off the Saran wrap and examined the lichen samples with a magnifying glass, took pictures, and wrote down my observations in my log book. After doing this, I misted the plants again and replaced the Saran wrap. I did this repeatedly for ten days. I then performed the experiment again with new lichen samples keeping all the variables the same. I recorded all my observations in my log book.

Test 1 Control (on left) and Acidic (on right)

Test 2 Control (on left) and Acidic (on right)

Conclusion

The testing of the effect of acidic solution of fruticose, foliose, and crustose lichens, showed that there is a variation in the way acid rain effects these different lichens in the natural environment. The crustose lichens survive well in the hostile acidic environment. The fruticose lichens do not fair as well and do not grow to their full potential of size or beauty while being effected by acid rain. The foliose lichens do not do well at all. Instead of being tall, deep colored lichens, the foliose became dry and brittle, not nearing the growth of what they could be in a clean environment. The experiment also illustrated that all three types of lichens can be used as bioindicators. Wherever flourishing crustose lichens are formed, the area is polluted because the crustose survive well in unhealthy environments. Where thriving foliose and fruticose lichens can be found, the environment is clean and healthy. If there was acid rain polluting the area, the lichens would lose their beauty and stop growing to their potential.

Discussion

In both the first and second runs of the experiment, the data presented results that showed the acidic solution had a serious affect on the fruticose, foliose, and crustose lichens. In both tests, the control samples of the fruticose and foliose lichens grew well and turned healthy colors. Since the lichens have no stems or roots they are forced into getting their nutrients from the air around them. The control lichen samples were receiving clean bottled water which they feed on. The crustose control lichen sample seemed unaffected by the clean water environment. In both tests, the crustose lichens neither declined of grew, but just stayed the way they were from the first day of experimenting. The lichens fed with acidic solution differed in their growth over the ten days. The fruticose and foliose samples did not grow nearly as well as the control samples and turned drab, unhealthy colors. They were taking in nutrients from the air around them which was acidic and unhealthy. The crustose lichens fed with acidic solution grew well and even turned a nice green color. Some lichens, like the crustose, are known to sometimes grow well in these hostile environments and can survive as the crustose samples in both tests did.

The results of the experiment partially supported the hypothesis. The crustose lichens were the least susceptible to the acidic solution. The fruticose samples were not the most susceptible to the acidic solution. The acidic solution did affect the growth of the thalluses, but neither the crustose or the fruticose lichens were affected as severely as the foliose lichens. While they should have had deep orange thalluses that grew at an amazing rate, the foliose lichens fed with acidic solution had only burnt ends on their thalluses and didn't grow upward at all.

The results of the experiment also support the hypothesis that these lichens can be used as bioindicators. By knowing that the fruticose and foliose lichens do not grow well in acidic environments, scientists can tell where pollution is and is not. For example, the results show that where the fruticose and foliose population are low, and the crustose lichen population is high, there is acid rain pollution in the area.

This project could be extended by changing the levels of acidity the solution has. By observing the growth of the lichens in an unhealthier environment, it may be possible for scientists to set up guidelines in order to determine just how polluted an area is. As the experiment is repeated and revised, it could also be improved. In devising a way to measure the actual growth of the lichens, the experiment would be even more accurate and valid.