Background Information
I personally chose to investigate this topic because green beans are one of my favorite vegetables to eat, and I have tried to grow them several times with varying degrees of success. Because I was sometimes not able to grow the plants from seeds, I was interested in what variables could affect the seedlings’ growth, specifically soil amendments such as vermiculite or perlite. Because of this, I decided to investigate how the concentration of vermiculite in soil affects seedling survival of green bean, also known as Phaseolus vulgaris, seeds.
Before a seed begins to grow, it goes through a period of dormancy, where it is incapable of germinating, even under favorable conditions (Bentsink & Koornneef, 2008). In order to break this period of dormancy, the seed’s environment must contain optimal amounts of light, oxygen, temperature, and water, among other factors. (Seed and Seedling Biology, n.d.). In some cases, other germination-promoting factors such as light treatment, stratification, after-ripening, and applied chemicals can also cause seeds to overcome dormancy (Bentsink & Koornneef, 2008).
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The process of germination begins with the stage of imbibition, where the seed begins to rapidly take up water, causing the outer seed coat to swell and soften (Seed and Seedling Biology, n.d.). Water uptake in the imbibition stage is triphasic, with the seed initially taking up water rapidly, then plateauing, then later further increasing its uptake (Bentsink & Koornneef, 2008). The next stage of germination is the interim or lag phase. In this stage, the seed initiates its internal processes, including cellular respiration, protein synthesis, and metabolization of food stores within the cell. (Seed and Seedling Biology, n.d.). Finally, the seed enters the third stage of germination, radicle and root emergence. In this stage, cells within the seed begin to elongate and divide, pushing the root and radicle out of the seed (Seed and Seedling Biology, n.d.).
After the process of germination, early seedling development begins. In dicots, or two-seed leaves, such as Phaseolus vulgaris, t he radicle attaches the plant to the ground and begins to absorb water from the substrate (Seed and Seedling Biology, n.d.). After this, the shoot emerges from the seed. The shoot is made up of 3 parts, the cotyledons, or seed leaves, the
hypocotyl, which is the section of shoot below the cotyledons, and the epicotyl, which is the section of shoot above the cotyledons (Seed and Seedling Biology, n.d.). In species of beans such as Phaseolus vulgaris, t he seed undergoes epigeal germination, in which the hypocotyl forms a hook which pulls the cotyledons and epicotyl to the surface of the soil. After this, the hypocotyl straightens, pulling the rest of the shoot into the air (Seed and Seedling Biology, n.d.). (Seed Germination, n.d.)
In my investigation, I will be exploring the effect of vermiculite concentration within the substrate as it relates to seed germination, seedling growth, and survival. Vermiculite is a natural compound of the chemical formula (Mg,Fe++,Al)3(Al,Si)4O10(OH)2•4(H2O), and is mined across the United States and the rest of the world (Barthelmy, n.d.) Horticultural vermiculite is commonly used in agriculture, as it improves soil aeration while retaining necessary moisture and nutrients for plant growth (Horticultural Uses, n.d.). Vermiculite is particularly effective in seed germination, as it increases the availability of oxygen and water, two necessary components to germination, increasing germination rates when it is utilized (Horticultural uses, n.d.)
The relationship between vermiculite and seed growth has been previously investigated in some species. A 2015 study found that when Plukenetia volubilis L. seeds were grown either sand or vermiculite, the seedlings in vermiculite had a 98% survival rate, while while the survival rate of seedlings grown in sand was only 79%. (Cardoso, Obolari, Borges, Silva, & Rodrigues, 2015).
In my exploration, I will study the effect of vermiculite on Phaseolus vulgaris germination and seedling growth. Phaseolus Vulgaris, commonly known as a french bean, best grows in a sunny, warm position, in light, well drained soil, and prefers a ph between 5.5 and 6.5 (Phaseolus Vulgaris, n.d.).
Hypothesis/Explanation
Increasing the concentration of vermiculite within the substrate will increase germination rate and seedling survival, but only until a certain point, at which the substrate will lack the necessary nutrients for plant growth normally supplied by soil, in turn decreasing seedling survival. This is because vermiculite increases aeration of the soil while also retaining water. Water retention is essential to germination and seedling development, as germination is started in the imbibition phase by rapid water absorption, and water is necessary for photosynthesis, the process by which plants convert sunlight into glucose. Soil aeration is also essential, as oxygen is necessary to overcome seed dormancy, as well as in cellular respiration, the process by which the plant’s cells convert glucose to usable energy in the form of ATP.
Overview
After recording all data, I decided that processing the average heights and standard deviations of the seedlings at each concentration, as well as processing the germination rates of the seeds at each concentration would best help to interpret the raw data. Through calculating the average height of the seedlings at each concentration by addition and division by the number of trials, I was able to come up with one value for height for each concentration that could be compared to that of others. By calculating the standard deviation of the data, I was also able to represent the variation within the data with 1 value for each concentration. Finally, in calculating the germination rate by dividing the number of seeds germinated over the total number of seeds, I was able to show the effect of the independent variable on seed germination.
Evaluation
The above data support the hypothesis that increased vermiculite concentration within the substrate, to an extent, increases seedling growth and germination rate in Phaseolus vulgaris seedlings, with the most effective concentration being 50% vermiculite to 50% soil. In the experiment, seeds planted in the 50% vermiculite mixture grew to an average height of 31.7 cm after 14 days as compared to an average height of 21.5 cm achieved by seeds planted in a 100% soil substrate. Seeds planted in the 50% mixture also demonstrated higher germination rates in than seeds planted in only soil, 95.8% in the optimal mixture as compared to 75% without any vermiculite added. With concentrations higher than 50% vermiculite, seedling growth did suffer dramatically, with the worst performing seedlings in the 75% and 100% vermiculite ranges. The differences in seedling height and germination rate are also statistically significant, as the 2 sample T test yielded a p value of .07 when comparing the average heights of the seedlings planted in 0% and 50% vermiculite substrates, and the 2 sample Z test yielded a p value of .02 when comparing germination rates at the same concentrations. Both p values point to a statistically significant difference at the 90% confidence interval, and the .02 value for germination rates remains significant at the 95% confidence interval.
Based on previous research, the results of the experiment reflect the scientific basis upon which the hypothesis that plant growth would improve, to an extent, with increased vermiculite within the substrate. This hypothesis was based on the fact that vermiculite increases aeration of the soil while also retaining water (Horticultural Uses, n.d.). Water retention is essential to germination and seedling development, as germination is started in the imbibition phase by rapid water absorption, and water is necessary for photosynthesis, the process by which plants convert sunlight into glucose (Seed and Seedling Biology, n.d.) . Soil aeration is also essential, as oxygen
is necessary to overcome seed dormancy, as well as in cellular respiration, the process by which the plant’s cells convert glucose to usable energy in the form of ATP (Seed and Seedling Biology, n.d.) .
Despite producing relatively consistent data, the experimental design of the investigation did have some flaws. First, the only measurement of seedling growth used was height, while other factors such as mass, stem thickness, and more could have been used to measure the growth of the seedlings. Also, as in any experiment, more trials could have been performed in order to increase the accuracy of the results. Finally, the investigation only addressed 5 concentrations of vermiculite within the substrate, meaning that the ideal concentration of vermiculite for Phaseolus vulgaris s eedling growth could not have been tested in the experiment.
In a future version of the investigation several changes could be made. First, after the 2 weeks of growth, plants could be removed from the substrate and weighed to measure growth. Root lengths could also be measured in order to better measure seedling development. Again, more seedlings could also be grown in order to produce more accurate results. After analyzing the results of the investigation, additional research questions can be proposed. One such question related to the experiment would be to analyze the differences in seedling growth in different soil amendments, including lime, fertilizers, vermiculite, gypsum, and clay. While the previous investigation only addressed the effects of vermiculite on seedling development, this investigation would compare the effects of different amendments and blends in order to determine the most efficient substrate composition.
Works Cited
- Barthelmy, D. (n.d.). Vermiculite Mineral Data. Retrieved September 14, 2018, from http://webmineral.com/data/Vermiculite.shtml#.W5vFl2hKjrc
- Bentsink, L., & Koornneef, M. (2008, December 30). Seed Dormancy and Germination. Retrieved September 13, 2018, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3243337/
- Cardoso, A., Obolari, A., Borges, E., Silva, C., & Rodrigues, H. (2015, June). Environmental factors on seed germination, seedling survival and initial growth of sacha inchi (Plukenetia volubilis L.). Retrieved September 13, 2018, from http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2317-15372015000200111
- Horticultural Uses of Perlite and Vermiculite. (n.d.) Retrieved October 4, 2018, from http://www.schundler.com/hort.htm
- Phaseolus vulgaris - L. (n.d.). Retrieved September 13, 2018, from https://pfaf.org/user/plant.aspx?LatinName=Phaseolus vulgaris
- Seed and Seedling Biology. (n.d.). Retrieved October 4, 2018, from https://extension.psu.edu/seed-and-seedling-biology
- Seed Germination. (n.d.) Retrieved October 4, 2018, from https://staff.guilan.ac.ir/staff/users/jolfati/fckeditor_repo/file/%D9%81%DB%8C%D8% B2%DB%8C%D9%88%D9%84%D9%88%DA%98%DB%8C%20%D8%B3%D8%A8%D8%B2%DB%8C%D9%87%D8%A7/SEED%20GERMINATION_ppt%20%5bComp atibility%20Mode%5d.pdf
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