Background Research on Seeds

Before germination, a seed goes through a resting period called dormancy. Germination of seeds is a complex physiological process that starts by imbibition of water after possible dormancy mechanisms have been released by the appropriate triggers, meaning that it resumes growth, bursting through its encasing. (The Seed Biology Place, 2009) This coat acts to protect the internal embryo from the elements, parasites and mechanical injury while it is still dormant (Washington State University 1999). Germination can only take place under specific circumstances, involving suitable temperature, oxygen supply, water, and sunlight. For a seed to germinate, it takes different times depending on the species, although this can be speed using various methods.

Dormancy is “a condition typified by extremely low metabolic rate and suspension of growth and development” (Urry, Cain, Wasserman, Minorsky & Reece, 2017) In plants, dormancy is caused by many factors, including light, temperature, moisture and the presence of Abscisic Acid (ABA), that slows growth, promoting seed dormancy. (Urry, Cain, Wasserman, Minorsky & Reece, 2017) All these things would be typically overcome in the seed’s natural environment. Thus, it is important to maintain water, oxygen and temperature and optimum levels for germination.

Temperature is important, as it can affect the presence of germination inhibitors (RCN 2004). When the temperature is not ideal, these chemicals continue to prevent the continuation of growth of the embryo, to ensure that the seed germinates under favorable conditions for continued growth and metabolism. The favored temperature for germination varies greatly between plant species, depending on their environment.

If there is an insufficient supply of oxygen, germination may not take place (Aggie Horticulture 2009). Oxygen is a requirement for respiration, meaning that a lack thereof will cause the plant to die soon after germination.

Before the embryo can burst out of his coat, there is a large intake of water that helps the embryo to expand and burst through its casting (Washington State University 1999).
Light is also a factor for some plants, as plants require it for photosynthesis to occur. When buried too deeply, the plant will die eventually due it runs of the food supply that could not de replenish (Aggie Horticulture 2009).

Plants have a tolerance level for the salinity of their substrate, within which they will germinate. Soil and water both have small concentrations of salt naturally present, which plants have developed to tolerate (ABC 2006).

Question

Is Will increasing the salinity of the substrate negatively affect the rate of black bean seed germination?

Variables

Independent Variable

Five trials will be done with the following concentrations of solution:

1. 0.00%
2. 0.25%
3. 0.50%
4. 0.75%
5. 1.00%

Dependent Variable

Number of days for seeds to germinate.

Controls

Amount of Water – All the seeds will be given 100mL of water at planting, and they were not given anymore. They will all be receiving the same amount of water with different concentrations of salt. Water is retained by laying transparent plastic wrap over the containers to prevent water from evaporating off.

• Salt – ‘La Fina’ iodized table salt will be used in all soils that are being treated with salt.
• Seeds – ‘Yates’ broad bean Vicia faba seeds will be used throughout the entire experiment.
• Water – The water used on the seeds will be sourced from the same tap for the entire experiment. This is to reduce any variation in levels of chlorine and other substances, which may affect them.
• Sunlight – All the seeds will receive the same amount of exposure to sunlight. They will remain in the same area all the time, meaning that there will be no variation between groups. The amount they receive cannot be measured, but as it is constant, it will not be a factor in any difference between the results of each test.
• Temperature – The temperature of the seeds’ environment will be controlled by keeping the seeds in the same area.
• Substrate – The soil used for the experiment was the same for all the trials. All other substrates, such as soil, would naturally have a low salt concentration, altering the concentration the seeds would be exposed to.

Materials

• 50 x black bean Phaseolus vulgaris seeds
• 5 x take-away containers – 11x16cm
• 5 liters of tap water
• La Fina iodized table salt
• 1-litre beaker
• 1 500 ml beaker
• Electronic balance
• Black permanent marker pen
• Metal stirring rod
• Transparent plastic cling wrap
• Eco substrate, substrate orgánico Multi-Purpose Potting Mix

Method

1. The side of each takeaway container was marked with the number 1 to 5 with the marker pen, to indicate which concentration it contained.
2. Each container was filled with potting mix to a depth of 2cm.
3. Ten broad bean seeds were placed in each container, pressed into the soil so that they were partially covered by the potting mix.
4. Washed 1-liter beaker then filled with 1-litre tap water, taking care that no parallax error was made in reading.
5. For the first solution, no salt was added, so 100mL of the water was measured in the 500mL beaker, then poured over the substrate in a container marked 1.
6. Washed the beaker, and then filled with 1 liter of tap water from the same source. Exactly 2.60g salt was measured on the electronic balance and added to the water to make a concentration of 0.25%, and then stirred with the rod until the salt dissolved.
7. 100mL of the salt solution was measured into the 500mL beaker, then poured over the substrate in container 2.
8. This procedure was repeated 3 more times, washing the beaker to remove any residual salt. 5.00g, 7.60g, and 10.20g of salt were added in turn for concentrations of 0.50%, 0.75%, and 1.00% respectively.
9. Once all the samples had been watered, they were placed in an outdoor area. During the day, they received direct sunlight. They were not exposed to any additional artificial light.
10. The transparent plastic film was placed over the containers to prevent water from evaporating. Airflow was still allowed.
11. The samples were examined daily to see if any of the seeds had germinated. This was indicated by the rupture of the encasing and a visible plant root. The total number of germinated seeds was recorded each day for 10 days.