The effect of mycorrhizae on the growth rate of Raphanus sativus (radish)
Phillip C. Sargent
Department of Biological Sciences
Saddleback College Mission Viejo, CA 92692
Abstract
Mycorrhize is a type of fungus found in the phylum Zygomycota. It is generally known for forming mutualistic relationships with plant roots where the mycorrhizal fungus provides the inorganic nutrients 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 are not infected with the fungus. This leads to the question of what would be the effect of a large volume of mycorrhizal fungus added to a low phosphorous/low fertilized environment on the growth rate of plants. Twenty seven Raphanus sativus seeds were planted in nine pots, three to a pot. These pots where divided into three groups. Control, which had no mycorrhizal fungus in the soil, and two others with mycorrhizal fungus; 5 mL and 10 mL. After all seeds in the pots had germinated one plant was chosen to use and the others were uprooted. These were 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, 10mL groups in number of leaves or in leaf length.
Introduction
Fungi are often associated mostly with decomposers and parasites. However there are certain species of fungi which are under the category of mycorrhize. This group is found in the Phylum Zygomycota and generally forms a mutalistic relationship with plant root systems. This is achieved by the process of the fungus increasing the plants phosphorus intake along with other inorganic resources by extending specialized structures called Haustoria in to cells plant. 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 also has the potential to be harmful to plants in more extreme environments (Reynolds, et. al.,2004) such as too much fertilizer (Johnson, 1993) or 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 to regeneration of overused land, such as former mines. This could also be beneficial in burned areas. For example, a study in 1988 revealed (Klopatek et. al.) that fire lowered the arbuscular mycorrhizae content in the soils. 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 was specifically focused on the micorrhizal fungus on growth rates of the plants infected with large amounts the fungus in poorer 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 try to determine if doubling the concentration of mycorrhizal fungus will double the growth rate when the fungus’s concentration is doubled. The expectation was that there would be a significantly greater difference between the growth rates of a plant with a soil with mycorrhiaze than a plant with a soil without the fungus due to the increased nutrient intake. 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 plain dirt. This was done to ensure that the plants would contain similar low fertilized soil conditions (Johnson, 1993). The mycorrhizal 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 are 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. These seeds were placed be approximately four centimeters apart from each other and one centimeter deep. The plants will be 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, where their leaf length was measured once a week by measuring from stem to the tip of the leaf through the middle of the leaf with a standard 30cm ruler. The leaves were measured from the outermost leaves to the inner leaves last measured. Also the number of leaves the plant had was tracked. Throughout the four weeks the water the plants received was constant even though the time between watering was not. When watering, all the plants were watered at the same time. After the four-week period was over 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 of leaves measured throughout the growth periods of four weeks. Type one was the first to sprout, and type two was soon to follow however only two grew of each of those types. The type three leaves were the last to grow but grew the most number of leaves. The average number of leaves was recorded in an table 1.
Control / 5 mL / 10 mL24-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. An simple ANOVA, one-way, test was run finding 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.(ERROR BARS)
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 three leaves were chosen for analysis of growth rate for two reasons. They were the main leaves of the plants and they were the fastest growing leaves of the plant.
Leaf type / Control / 5 mL / 10 mLAverage 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 size 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. This Data was entered in an Microsoft Excel spreadsheet and an simple ANOVA, one-way, stats test was run. This also confirmed that there was no significant difference (p= 0.9689) in growth rate between the two groups that had mycorrhize and those that did not. Further more there was no significant difference between the control group and the mycorrhize groups.
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 can be many reasons that there was no significant difference between the three groups. One major aspect was the That the control group 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 played with the result of the experiment. The low fertilized garden soil was mixed with plain unfertilized soil to ensure an low fertilized environment. One pot in the 10ml section ended up not growing so a transplant from the same test group was put in its place. This died as well. This is most likely due to the transplant shock in which the plant never fully took root again. This should not because lack of water, which has been shown to affect the amount of plant growth in an 2010 study by Franzini, Vinicius Ide, Rosario Azcón, et. Al.(format) Which found that at medium drought level the negative effects growth rate by the micorrhizal fungus were dependant on the Phosporus levels. It might be possible that the plants had an adverse reacton in order to protect it self from the Mycorrhizal fungus. For example, in a study in published in 2011, in the FEMS Microbiology Ecology found that Trichoderma harzianum was an active biocontrol agent that defends a plant from plant infections. This included mycorrhizal infections, and which indirectly affected plant growth.
Position and location
The position of the Raphanus sativus plants appears to be a key factor in the growth rate of the plant. This has a big affect on the amount of sunlight that a plant receives. This may have been the case because the back row of plants grew bigger earlier. Where as 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 weather affects. 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. 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. 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 probably 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. This is a possible explanation for the decrease in growth rate as it rained around the sheltered plants the temperature could have dropped lowering the average growth rate.
The humidity also is hypothesized to play a big role in the Raphanus sativus growth rate. This, along with ambient temperature, was not tracked. This effect is confirmed in a study preformed in 2009 by Greek scientists (Karamanos et al.) looking at the affects of drought treatments. That found that at higher temperatures Lucerne (Medicago sativa L.) during its flowering period lead to a longer flowering period and a higher number of inflorecences?. The study concluded with saying that the effects of the growing season was more important than the drought water treatments.
Future Studies
These findings it would be interesting to study the growth rate of the growth rate of the plant with mycorrhizal fungus at different temperatures to see if the mycorrhizal fungus actually hinders the plant growth when the plants reach their upper and lower critical limits, as this would test the mycorrhizal fungus’s relationship to the plant. This would be used to see if the mycorrhizal fungus turns into a parasitic nature instead of a beneficial one.
References
De Jaeger, Nathalie, Ivan E de la Providencia, Hervé Dupré de Boulois, and Stéphane Declerck. 2011. "Trichoderma harzianum might impact phosphorus transport by arbuscular mycorrhizal fungi." FEMS Microbiology Ecology 77, no. 3: 558-567.
Franzini, Vinicius Ide, Rosario Azcón, Fernanda Latanze Mendes, and Ricardo Aroca. 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, Nancy Collins (November 1993) Can Fertilization of Soil Select Less Mutualistic Mycorrhizae Ecological Applacations, Vol 3, No. 4 pp. 749-757
Reynolds, Heather L., Vogelsang, Keith M., Hartley,Anne, Bever,E. James D., Schultz, P. A. (Mar., 2006) Variable responses of old-field perennials to arbuscular mycorrhizal fungi and phosphorus source Oecologia, Vol. 147, No. 2, pp. 348-358
Karamanos, A. J., P. T. Papastylianou, J. Stavrou, and C. Avgoulas. 2009. "Effects of Water Shortage and Air Temperature on Seed Yield and Seed Performance of Lucerne ( Medicago sativa L.) in a Mediterranean Environment." Journal Of Agronomy & Crop Science 195, no. 6: 408-419.