The Effect of Mycorrhizae on the Growth Rate of Raphanus sativus




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The Effect of Mycorrhizae on the Growth Rate of Raphanus sativus

Phillip C. Sargent



Department of Biological Sciences

Saddleback College



Mission Viejo, CA 92692
Mycorrhize is a type of fungus found in the phylum Zygomycota. It is generally known for forming mutualistic relationships with plant roots. The mycorrhizal fungus provides the inorganic nutrients for the plant, and in return the plant gives the mycorrhizal fungus the nutrients necessary to survive. This relationship has been shown to increase the plants inorganic nutrient intake, which allows the plant to grow bigger than plants that do not form this mutualistic relationship. The current study sought to determine whether a large volume of mycorrhizal fungus added to a low phosphorous/low fertilized environment would have an effect on the growth rate of the plants. Twenty-seven Raphanus sativus seeds were planted in nine pots, three seeds to a pot. These pots where divided into three groups: the control group which did not contain any mycorrhize fungus in the soil, group 1 which had 5mL of mycorrhize, and group 2 which contained 10mL of mycorrhize. Was the mycorrhize dissolved in water, is that why it is in mL? Explain how you administered the fungus. After all of the seeds in the pots had germinated one plant was chosen to use and the others were uprooted. The solitary plant in each pot was allowed to grow for four weeks being measured once each week in number of leaves and length of leaves. After the four weeks the plants growth rate was calculated in each category. These were tested in an ANOVA test. It was found that there was no statistical difference between any of the control, 5 mL, or 10mL groups in number of leaves or leaf length.
Introduction
Fungi are often associated with being decomposers and parasites. However there are certain species of fungi that are under the category of mycorrhize. This group of fungus is found in the Phylum Zygomycota and generally forms a mutalistic relationship with plant root systems. The fungus provides benefits such as increasing the plants phosphorus intake along with other inorganic resources. It does so by extending specialized structures called haustoria into the plants cells. In return the plant provides the nutrients needed for the fungus to survive (Marschner 2002). Mycorrhizal fungus can be beneficial as long as the net gain of the plants resources is positive. However, at times, mycorrhizal fungus has the potential to be harmful to plants in more extreme environments (Reynolds, et. al.,2004). One such environment that fungus can be harmful is one in which there is too much fertilizer (Johnson, 1993). Another would be during periods where resources are scarce, such as drought (Franzini et. al.,2010). An example of a beneficial reaction to mycorrhizal fungus was found in 1979 by researchers Thomas Moorman and F. Brent Reeves, who found the mycorrhizal fungus is beneficial in regenerating of overused land, such as former mines. Mycorrhizal fungus can also be beneficial in burned areas. For example, a study in 1988 revealed that fire lowered the arbuscular mycorrhizae content in the soilsKlopatek et. al.). The results will however depend on the types of mycorrhizae used as the beneficial properties vary from plant to plant. This is because it was found in 2011 that crop growth such as maize were affected by different Mycorrhizae types (Ortas, I.,& Akpinar, C. 2011). Also, in highly fertilized situations a faster growth rate is experienced (R. T. Lamar and C. B. Davey (1988)).

This study specifically focused on the effect of micorrhizal fungus on growth rates of the plants exposed to large amounts of the fungus in poor soil conditions. This research is vital because of the potential it poses to speed up crop growth in poorer soil conditions with limited amount of fertilizer necessary. This study was also commenced to determine if doubling the concentration of mycorrhizal fungus would double the growth rate when the fungus concentration is doubled. The expectation of this experiment is that there will be a significantly greater difference between the growth rate of a plant with mycorrhizae fungus in the soil than a plant without the mycorrhizae because of the increased nutrients the fungus provides to the plant. This should be in accordance with a study by Roger T. Koide in 1991, who found similar results. They found that the mycorrhizal fungi increased plant growth. The research also predicted that there would be no significant difference between the two mycorrhizae groups growth rate in the long term.


Materials and Methods
The soil chosen was a mixture of dirt out of the Sargent’s Garden mixed in with regular dirt. This was done to ensure that the plants would contain similar low fertilized soil conditions (Johnson, 1993). The mycorrizal fungus was added and mixed into the soil prior to planting the seeds. The soil was split into three groups; two with mycorrizal fungus and one without the fungus acting as the control group. The two with mycorrhiaze were split into one group with 5ml and one with 10ml of mycorrhizal fungus. The pots were then labeled. Control was the group with no mycorrhizal fungus added. The group with 5ml mycorrhizal fungus added was labeled 1x. Finally, the 10ml group was labeled 2x. Each group was split further into three tests to differentiate between each pot. Then twenty-seven Raphanus sativus seeds were chosen from a bag of seeds purchased from Home Depot. Three seeds were placed into an individual pot. The seeds were placed approximately 4cm apart and one centimeter deep. The plants were allowed to germinate till each pot had at least one plant, and then two plants per pot were removed leaving one plant per pot. The plants were allowed to grow for a period of four weeks. The leaf length of each plant was measured once a week by measuring from stem to the tip of the leaf with a 30 cm ruler. The leaves were measured from the outermost leaves to the innermost leaves measured last. The number of leaves the plant had was also tracked. Throughout the four weeks the water the plants received was constant however the time between watering was not. When watering, all the plants were watered at the same time. After the four-week period the plants were dug up and their mass was measured. This data was then used to calculate growth rate.
Results
There were three leaf types measured throughout the growth period of four weeks. Type 1 was the first to sprout followed by the Type 2 leaves. Only two plants with Type 2 leaves grew, however. The Type 3 leaves were the last to grow, but were the most numerous. The average number of leaves was recorded in table 1.





Control

5 mL

10 mL

24-Oct

3.3

4

4.3

30-Oct

4.7

4.7

6

5-Nov

7.0

7.0

7.0

11-Nov

7.0

8.0

9.0


Table 1. The average number of leaves the plant produced in the four-week growth period.
This data was divided by time in days to find the growth rate of the plant. A simple ANOVA, one-way test was run. These findings show that there was no significant difference in the growth rate of the plant (p= 0.89954).



Figure 2. The average growth rate of the plant leaves number. There was no significant difference found (p= 0.8995). Included is the mean standard error.
Leaf length was also tracked during the growth period. This was done to ensure that the results obtained were confirmed. These values were logged by leaf type and then were averaged out and entered in table 2. The type 3 leaves were chosen for analysis of growth rate for two reasons: they were the leaves that were the most numerous on the plant, and the fastest growing.


Leaf type

Control

5 mL

10 mL




Average length (cm)

Average length (cm)

Average length (cm)




24-Oct







1

1.22

1.3

1.8

2

2.73

1.5

3.08

3

0

0

0




30-Oct







1

1.4

1.37

1.78

2

4.9

3.13

4.15

3

2.88

2.65

3.22




5-Nov







1

1.5

1.5

1.95

2

3.8

3.9

4.8

3

4.34

3.5

3.63




11-Nov







1

1.5

1.42

D

2

4

4.67

4.3

3

4.63

4.14

4.93


Table 2. A table of the average leaf length of the plant in a four-week period. The D symbol means that those leaves have died off.
The Type 3 leaf results were also divided by time to obtain the growth rate of the leaves. These data were entered in an Excel spreadsheet and a simple ANOVA, one-way stats test was run. This test also confirmed that there was no significant difference (p= 0.9689), in growth rate between the groups that had mycorrhize and the control group.



Figure 3.The average growth rate derived from leaf size. There is no significant difference between any of the groups (p= 0.96893). Included is the mean standard error.
Discussion
There are many possible reasons why there was no significant difference between the three groups. One major aspect was that the control group germinated faster. (Maybe explain why the control germinated faster). This gave the control a head start when measurements were taken. This lead some of the growth rate averages to be off because the control already had some well established leaves.
Soil Conditions

Soil conditions could have affected the results of the experiment. The low fertilized garden soil was mixed with regular unfertilized soil to ensure a low fertilized environment. One pot in the 10mL group ended up not growing, so a transplant from the same test group was put in its place. This plant died as well, however. This is most likely due to the transplant shock in which the plant never fully took root again. Lack of water has also been shown to affect the amount of plant growth. In a 2010 study by Franzini, Vinicius Ide, Rosario Azcón, et. Al., it was found that at medium drought levels the negative growth rate by the micorrhizal fungus were dependant on the phosphorus levels. It could be possible that the plants had an adverse reaction in order to protect itself from the mycorrhizal fungus. For example, in a study published in 2011, in the FEMS Microbiology Ecology, it was found that Trichoderma harzianum was an active bio-control agent that defends a plant from infections. This includes mycorrhizal infections, which indirectly affects plant growth.


Position and location

The position of the Raphanus sativus plants appears to be a key factor in the growth rate of the plants. Position has a big affect on the amount of sunlight that a plant receives. This factor may have played a significant role in the results of the experiment because the back row of plants grew bigger earlier, whereas the plants in the front grew less. The plants were placed in a triangle formation on a bench under a balcony. All the plants received adequate amount of light and were protected from most negative weather conditions. It was noted early on that the back row of Raphanus sativus plants were more sheltered and had less sun than the front row of three plants. Then wouldn’t the plants in the back row grow less if they received less sunlight? It is stated that they grew more than the plants in the front, but the ones in the front received more sunlight? Consider revising. This is also why the lower leaves had a hard time growing because they could not get enough light from over the lip of the pot. However once the leaves crested the lip of the pot the size of leaves grew faster. Than the leaves in the front receiving more sunlight? These plants probably retained their water longer thus avoiding drought like conditions described in Franzini’s study.


Ambient Temperature

Ambient Temperature is an important factor that could have contributed to the results of this experiment. This study was done outside and as such, air temperature is less constant than plants grown inside a green house. Therefore fluctuating temperatures and periodic rain could explain a decrease in growth rate during these more extreme weather conditions.

The humidity also is hypothesized to play a significant role in the Raphanus sativus growth rate. Humidity, however, along with ambient temperature were not tracked throughout this experiment. Humidity’s effect on plant growth is confirmed in a study preformed in 2009 by Greek scientist Karamanos, A. J., by looking at the effects of drought treatments. This study found that higher temperatures during a plants flowering period leads to a longer flowering period and a higher number of inflorescences

( Medicago sativa L.). The study concluded with saying that the effects of the growing season were more important than the drought water treatments.


Future Studies

In future studies it would be interesting to study the growth rate of the plant with micorrhizal fungus at different temperatures. Micorrhizal fungus would be used to determine if it hinders plant growth when the plant’s reach their upper and lower critical limits of temperature. This study would test the micorrhizal fungus’ relationship to the plant, and if the micorrhizal fungus turns into a parasitic relationship instead of a beneficial one.


References
De Jaeger, N., Providencia I.E., De Boulois H. D., and Declerck S. 2011. Trichoderma harzianum might impact phosphorus transport by arbuscular mycorrhizal fungi. FEMS Microbiology Ecology, 77, no. 3: 558-567.
Franzini, Ide V., Azcón R., Mendes F.L., and Aroca R. 2010, Interactions between Glomus species and Rhizobium strains affect the nutritional physiology of drought-stressed legume hosts. Journal of Plant Physiology, 167, no. 8: 614-619.
Johnson, N.C. 1993, Can fertilization of soil select less mutualistic mycorrhizae? Ecological Applications, Vol. 3, No. 4: 749-757.
Karamanos, A. J., Papastylianou P. T., Stavrou J., and Avgoulas C. 2009, Effects of water shortage and air temperature on seed yield and seed performance of lucern in a mediterranean environment. Journal of Agronomy & Crop Science, 195, no. 6: 408-419.
Klopatek, Coe C., Debano, Leonard F., Klopatek, Jeffrey M.1988, Effects of simulated fire on vesicular-arbuscular mycorrhizae in pinyon-juniper woodland soil. Plant and Soil, Vol. 109, No. 2, 245-249.
Koide, Roger T. Tansley Review 1991, Nutrient supply, nutrient demand and plant response to mycorrhizal infection. New Phytologist, 117, no.29: 365-386.
Lamar, R. T. and Davey, C. B. 1988, Comparative effectivity of three fraxinus pennsylvanica marsh. Vesicular-arbuscular mycorrhizal fungi in a high-phosphorus nursery soil. New Phytologist, Vol. 109, No. 2: 171-181.
Marschner H (2002) Mineral nutrition of higher plants, 2nd edn. Elsevier Science Ltd, Great Britain
Moorman, Thomas, Reeves, Brent F. 1979, The role of endomycorrhizae in revegetation practices in the semi-arid west. A comparison of incidence of mycorrhizae in severely disturbed vs. natural environments. American Journal of Botany, Vol. 66 no. 1:6-13.
Ortas, I., and Akpinar, C. 2011, Response of maize genotypes to several mycorrhizal inoculums in terms of plant growth, nutrient uptake and spore production. Journal of Plant Nutrition, 34: 970-987.
Reynolds, Heather L., Vogelsang, Keith M., Hartley, Anne, Bever, E. James D., Schultz, P. A. 2006, Variable responses of old-field perennials to arbuscular mycorrhizal fungi and phosphorus. Oecologia, Vol. 147, no. 2: 348-358.

Review Form

Department of Biological Sciences

Saddleback College, Mission Viejo, CA 92692

Author (s): Sargent_________

Title: The Effect of Mycorrhizae on the growth rate of Raphanus sativus
Summary

Summarize the paper succinctly and dispassionately. Do not criticize here, just show that you understood the paper.


The main point of this experiment was to test if the fungus mycorrhizae can affect the growth rate of a certain plant (Raphanus sativus). Mycorrhizae are known to have a mutualistic relationship with plants at times, and this study sought to seek if that notion had any merit. The plants were divided into three groups: a control with no mycorrhizae in the soil, group 1 with 5mL of mycorrhizae in the soil, and group 2 with 10 mL of mycorrhizae in the soil. There were three subjects in each group. The number of leaves and length of the leaf on each plant was measured once a week for a four week period and the results indicated that there was no significant different in the plants growing soil with the mycorrhizae and the plants in the control group.


General Comments

Generally explain the paper’s strengths and weaknesses and whether they are serious, or important to our current state of knowledge.


I found the experiment to be very interesting and explained well. I got a good understanding of the methods used to execute the experiment and the materials used. The introduction clearly gave an idea of the role of mycorrhizae as a mutualistic partner, and how other studies came to this conclusion. It stated the main purpose of the experiment, and what the hypothesis was. The paper had several grammatical errors, however, and there where several run-on sentences. I got the main idea of what the author was saying, but at times it was a bit convoluted. A couple areas in the discussion were a bit confusing, like the position and location of the plant. The more sunlight usually produces more growth, but the paper says otherwise. I like that the discussion is organized into several subgroups, it makes the points easier to understand. I believe if the author reads through the paper and fixes some of the repetitive sentences and grammatical errors, it will be a very successful paper.

Technical Criticism

Review technical issues, organization and clarity. Provide a table of typographical errors, grammatical errors, and minor textual problems. It's not the reviewer's job to copy Edit the paper, mark the manuscript.


This paper was a final version X This paper was a rough draft

Notes have been made on the paper and are marked in red.




Recommendation
 This paper should be published as is

* This paper should be published with revision



 This paper should not be published


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